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Vol. 75, No. 1 (2026)

2026-01-05



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CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

  

COVER ARTICLE

Zero resistance and strange metal behavior of high-temperature superconducting material La3Ni2O7
In 2023, signatures of pressure-induced high-temperature superconductivity with an onset transition at 80 K were observed in La3Ni2O7. However, the absence of zero resistance cast doubts on its superconductivity. By using a recently developed quasi-hydrostatic pressure technique based on a diamond anvil cell, our group successfully observe a sharp superconducting transition with a zero resistance below 40 K, providing a crucial evidence for establishing the existence of high-temperature superconductivity in La3Ni2O7. Furthermore, a pronounced linear-temperature dependent resistivity is observed above its superconducting transition, suggesting an unconventional nature of its superconducting pairing state.In addition to the discovery of zero resistance, our transport study also revises the pressure-temperature phase diagram of La3Ni2O7. It is found that La3Ni2O7 remains metallic under pressure and there is no evidence for a metal-insulator transition if the samples are properly handled during preparations. Upon increasing pressure, the density wave transition, observed near 130 K at ambient pressure, is quickly suppressed. At approximately 13.7 GPa, evidence for a pressure-induced structural phase transition is observed near 250 K, followed by a superconducting transition with an onset temperature at $ T_{\mathrm{c}}^{\text{onset}}\approx $ 37.5 K. $ {T}_{\mathrm{c}} $ initially increases with the increase of pressure, reaching a maximum value of $ T_{\mathrm{c}}^{\text{onset}}\approx $ 66 K at 20.5 GPa. On the other hand, the slope $ {A}' $ of the T-linear resistivity above $ {T}_{\mathrm{c}} $ monotonically decreases with the increase of pressure, showing a relation of $ {T}_{\mathrm{c}}\propto \sqrt{{A}'} $ above 20.5 GPa, which is similar to those recently observed in the cuprate superconductors. Furthermore, the inverse Hall coefficient 1/RH, derived from the Hall resistance measurements, reveals a notable increase at pressures above 15 GPa upon entering the high pressure phase, suggesting a substantial increase of the carrier concentration in the superconducting regime, which is further supported by band structure calculations.In this work, we present a brief summary of our research advances, and compare them with those observed in other nickelate superconductors. YE Kaixin, ZHANG Yanan, JIAO Lin, YUAN Huiqiu Acta Physica Sinica.2026, 75(1): 010704.
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES
INTERDISCIPLINARY PHYSICS AND RELATED AREAS OF SCIENCE AND TECHNOLOGY
Review
ATOMIC AND MOLECULAR PHYSICS
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
 
Topics
CONDENSED MATTER: ELECTRONIC STRUCTURE, ELECTRICAL, MAGNETIC, AND OPTICAL PROPERTIES

COVER ARTICLE

Zero resistance and strange metal behavior of high-temperature superconducting material La3Ni2O7
YE Kaixin, ZHANG Yanan, JIAO Lin, YUAN Huiqiu
2026, 75 (1): 010704. doi: 10.7498/aps.75.20251207
Abstract +
In 2023, signatures of pressure-induced high-temperature superconductivity with an onset transition at 80 K were observed in La3Ni2O7. However, the absence of zero resistance cast doubts on its superconductivity. By using a recently developed quasi-hydrostatic pressure technique based on a diamond anvil cell, our group successfully observe a sharp superconducting transition with a zero resistance below 40 K, providing a crucial evidence for establishing the existence of high-temperature superconductivity in La3Ni2O7. Furthermore, a pronounced linear-temperature dependent resistivity is observed above its superconducting transition, suggesting an unconventional nature of its superconducting pairing state.In addition to the discovery of zero resistance, our transport study also revises the pressure-temperature phase diagram of La3Ni2O7. It is found that La3Ni2O7 remains metallic under pressure and there is no evidence for a metal-insulator transition if the samples are properly handled during preparations. Upon increasing pressure, the density wave transition, observed near 130 K at ambient pressure, is quickly suppressed. At approximately 13.7 GPa, evidence for a pressure-induced structural phase transition is observed near 250 K, followed by a superconducting transition with an onset temperature at $ T_{\mathrm{c}}^{\text{onset}}\approx $ 37.5 K. $ {T}_{\mathrm{c}} $ initially increases with the increase of pressure, reaching a maximum value of $ T_{\mathrm{c}}^{\text{onset}}\approx $ 66 K at 20.5 GPa. On the other hand, the slope $ {A}' $ of the T-linear resistivity above $ {T}_{\mathrm{c}} $ monotonically decreases with the increase of pressure, showing a relation of $ {T}_{\mathrm{c}}\propto \sqrt{{A}'} $ above 20.5 GPa, which is similar to those recently observed in the cuprate superconductors. Furthermore, the inverse Hall coefficient 1/RH, derived from the Hall resistance measurements, reveals a notable increase at pressures above 15 GPa upon entering the high pressure phase, suggesting a substantial increase of the carrier concentration in the superconducting regime, which is further supported by band structure calculations.In this work, we present a brief summary of our research advances, and compare them with those observed in other nickelate superconductors.

EDITOR'S SUGGESTION

Recent progress of two-dimensional van der Waals ferroelectric materials
LIU Bin, LIU Qing, PAN Er, BIAN Renji, LUO Xiao, LI Junpei, LIU Fucai
2026, 75 (1): 010809. doi: 10.7498/aps.75.20251367
Abstract +
Ferroelectric thin films and their device applications have drawn wide attentions since the 1990s. However, due to the critical size effect, ferroelectric thin films cannot maintain their ferroelectric properties as their thickness decreases to the nanometer size or one atomic layer, posing a significant challenge to the development of related nano-electronic devices. With a naturally stable layered structure, two-dimensional materials possess many advantages such as high-quality and smooth interface without dangling bonds, no interlayer interface defects, and the ability to maintain complete physical and chemical properties even at limited atomic thickness. Thus, it is gradually realized that two-dimensional materials are a good hotbed for the two-dimensional ferroelectricity. CuInP2S6, α-In2Se3, WTe2, and other intrinsic ferroelectric 2D materials have been reported successively while artificially stacked sliding ferroelectrics such as t-BN have also emerged, which expands the types of 2D ferroelectric materials and opens a new avenue for the further miniaturization and flexibility of ferroelectric electronic devices. This article reviews the recent research progress of two-dimensional ferroelectric materials, discusses their compositional characteristics, structural features and property modulation, and also prospects their application potential and future research hotspots.

EDITOR'S SUGGESTION

Machine learning empowered electronic structure calculations: Progress, challenges, and prospects
LI Yuting, YANG Jiong, XI Jinyang
2026, 75 (1): 010705. doi: 10.7498/aps.75.20251253
Abstract +
Density functional theory (DFT) serves as the primary method of calculating electronic structures in physics, chemistry, and materials science. However, its practical application is fundamentally limited by a computational cost that scales cubically with system size, making high-precision studies of complex or large-scale materials prohibitively expensive. This review addresses the key challenge by examining the rapidly evolving paradigm of integrating machine learning (ML) with first-principles calculations to significantly accelerate and expand electronic structure prediction. Our primary objective is to provide a comprehensive and critical overview of the methodological advances, physical outcomes, and transformative potential of this interdisciplinary field.The core methodological progress involves a shift from black-box property predictors to symmetry-preserving, transferable models that learn the fundamental Hamiltonian—the central quantity from which diverse electronic properties are derived. We detail this evolution, beginning with pioneering applications in molecular systems by using graph neural networks (e.g., SchNOrb, DimeNet) to predict energies, wavefunctions, and Hamiltonian matrices with meV-level accuracy. This review then focuses on the critical extension to periodic solids, where maintaining symmetries such as E(3)-equivariance and handling vast configurational spaces are of utmost importance. We systematically analyze three leading model families that define the state-of-the-art: the DeepH series, which uses local coordinate message passing and E(3)-equivariant networks to achieve sub-meV accuracy and linear scaling; the HamGNN framework, built on rigorous equivariant tensor decomposition, which excels in modeling systems with spin-orbit coupling and charged defects; and the DeePTB approach, which leverages deep learning for tight-binding Hamiltonian parameterization, enabling quantum-accurate simulations of millions of atoms.These methods yield significant physical results and computational breakthroughs. Key outcomes include: 1) unprecedented accuracy and speed. Models consistently achieve Hamiltonian prediction mean absolute errors (MAE) below 1 meV (e.g., DeepH-E3: ~0.4 meV in graphene; HamGNN: ~1.5 meV in QM9 molecules), along with computational speedups of 3 to 5 orders of magnitude compared with traditional DFT. 2) Scale bridging. Successful applications now range from small molecules to defect-containing supercells with over 10000 atoms (e.g., HamGNN-Q on a 13824-atom GaAs defect) and even to millions of atoms for optoelectronic property simulations (DeePTB). 3) Expanded application scope. This review highlights how these ML-accelerated tools are revolutionizing research in previously intractable areas: predicting spectroscopic properties of molecules (e.g., DetaNet for NMR/UV-Vis spectra), elucidating electronic structures of topological materials and magnetic moiré systems, computing electron-phonon coupling and carrier mobility with DFT-level accuracy but far greater efficiency (HamEPC framework), and enabling high-throughput screening for materials design.In conclusion, ML-accelerated electronic structure calculation has matured into a powerful paradigm, transitioning from a proof-of-concept to a tool capable of delivering DFT-fidelity results at dramatically reduced cost for systems of realistic scale and complexity. However, challenges remain, including model interpretability (“black-box” nature), transferability to unseen elements, and seamless integration with existing plane-wave DFT databases. Future directions include physics-constrained unsupervised learning (e.g., DeepH-zero), developing more universal and element-agnostic architectures, and creating closed-loop, artificial intelligence (AI)-driven discovery pipelines. By overcoming current limitations, these methods have the potential to fundamentally change the field of materials research, accelerating the process from atomistic simulation to rational material design and discovery.

EDITOR'S SUGGESTION

Dzyaloshinskii-Moriya interaction in rare-earth transition metal ferrimagnetic materials and spintronic applications
ZHANG Yu, MENG Gengchen, ZHAO Zhiyuan, LEI Na, WEI Dahai
2026, 75 (1): 010708. doi: 10.7498/aps.75.20251455
Abstract +
Magnetic exchange interactions and their induced magnetic structures are crucial factors in determining magnetization switching. Dzyaloshinskii-Moriya interaction (DMI) is an asymmetric exchange interaction arising from spin-orbit coupling and structural inversion symmetry breaking, which is one of the key mechanisms to induce non-collinear magnetic order and chiral magnetic structures, including magnetic Skyrmion, vortex and chiral domain wall. These magnetic structures enable novel information proceeding devices with ultralow power consumption. More importantly, non-collinear magnetic order exhibits richer and more novel physical behaviors than traditional collinear magnetic structures. With ongoing exploration and research into magnetic materials, rare-earth transition metal ferrimagnetic materials such as CoGd, CoTb, and GdFeCo have emerged as notable candidates. These materials combine the spin-orbit coupling of rare-earth elements with the magnetic exchange interactions of transition metals, leading to ultrafast magnetization dynamics, tunable magnetic structures, and rich spin transport phenomena. These properties provide an ideal material platform for studying and manipulating DMI, demonstrating significant potential in designing future high-density magnetic storage and spintronic devices. This review systematically elucidates the microscopic physical origin of DMI, outlines the fundamental characteristics of rare-earth transition metal ferrimagnetic materials, and explores the coupling mechanisms between DMI and ferrimagnetic order. We introduce the fundamental properties of RE-TM systems and their applications in spin logic devices and magnetic memory devices. We focus on discussing the physical phenomena related to DMI in RE-TM systems, including the scaling relationship of DMI in RE-TM, DMI-related spin-orbit torque effects, and the principles and applications of skyrmion-based devices, which will provide both theoretical foundations and technical guidance for the future development of advanced spintronic technologies.
Lattice-induced dual transparency in terahertz hybrid metasurfaces
HOU Yunfei, WANG Wenxian, ZHANG Yigong, XIONG Lei
2026, 75 (1): 010401. doi: 10.7498/aps.75.20250883
Abstract +
Electromagnetically induced transparency (EIT)-like phenomenon in terahertz (THz) metasurfaces facilitates flexible manipulation of electromagnetic wave transmission windows and enables light deceleration, rendering this phenomenon suitable for applications such as modulators, absorbers, slow light devices, and more. Traditional design methods focus on the coupling between bright-dark modes and bright-bright modes within the unit cell by leveraging interference cancellation effects to regulate electromagnetic wave transmission. Notably, the periodicity of the array structure also plays a pivotal role in adjusting the amplitude and resonance intensity of the transparent window, a phenomenon known as lattice-induced transparency (LIT). In this work, we introduce a gold nanorod structure and an S-shaped gold split-ring resonator supported on a vanadium dioxide (VO2) thin film to investigate LIT. Unlike traditional structures that solely consider single bright-bright or bright-dark mode coupling, our proposed structure integrates both bright-bright and bright-dark modes coupling. Furthermore, the dark mode in our structure is not a traditional multipolar mode but rather a surface lattice resonance (SLR) arising from the coupling between lattice modes and the localized surface plasmon resonance (LSPR) of the structure itself.Through the analysis of simulated transmission spectra for the individual gold nanorod and S-shaped split-ring structures, we observe that the gold nanorod exhibits LSPR at 0.985 THz, whereas the S-shaped split-ring structure demonstrates LSPR at 0.51 THz and SLR at 1.025 THz. When combined together, these structures form transparent windows with transmission rates of 66.03% at 0.643 THz and and 59.4% at 1.01 THz due to the interplay of bright-bright and bright-dark mode coupling. Upon examining the electric field distribution in the x-y plane, we find that the electric field energy is predominantly concentrated on the S-shaped split-ring.To gain deeper insights into each resonance mode, we employ multipolar decomposition to quantify resonance scattering energy. Our findings show that both transparent windows are predominantly governed by electric dipole scattering energy. Further investigations indicate that as the array structure’s period varies from 60 μm to 95 μm, the lattice mode progressively couples into the high frequency transmission valley (1.031 THz), giving rise to a high frequency hybrid mode (HFHM). The Q value of this mode initially increases and then decreases, peaking at 27 when the period is 84 μm. Similarly, as the period continues to increase, the lattice mode couples into the low frequency resonance valley (0.76 THz), forming a low frequency hybrid mode (LFHM) with a Q value that reaches a maximum of 51 at 115 μm—approximately one order of magnitude higher than that at a period of 60 μm. Additionally, as the periodicity increases, the near field coupling effect between adjacent units diminishes, leading to the gradual disappearance of the two transparent windows.To achieve active control over these transparent windows, we vary the conductivity of VO2 from 20 S/m to 30000 S/m, resulting in a decrease in the transmission amplitudes of the two transparent windows to 37.58% and 3.39%, respectively. Finally, we investigate the slow light effect of the two transparent windows and compare their maximum group delays, which are found to be 8.1 ps for each window. The terahertz metasurface proposed in this study paves the way for the design of future dynamically tunable sensing and slow light devices.

EDITOR'S SUGGESTION

Electronic properties and biaxial strain regulation of Janus-MoSSe/g-C3N4 heterostructures
HU Dong, LI Xiaobao, WANG Meiqin
2026, 75 (1): 010702. doi: 10.7498/aps.75.20251158
Abstract +
Constructing van der Waals (vdW) heterostructures has emerged as an effective strategy for enriching the physical properties of two-dimensional materials and optimizing their optoelectronic performance. In this work, we systematically investigate the electronic properties and biaxial strain modulation of Janus MoSSe/g-C3N4 heterostructures with two distinct interfacial configurations—SMoSe/g-C3N4 and SeMoS/g-C3N4—by means of first-principles simulations. Binding energy comparisons and AIMD simulations are performed to determine the most stable stacking pattern of each type of the heterostructure. The analyses of the electrostatic potential and work function reveal that the intrinsic dipole of MoSSe layer and the interfacial electric field in the SMoSe/g-C3N4 heterostructure undergo a constructive superposition. This enhances the overall built-in electric field, which points from g-C3N4 layer to MoSSe layer, resulting in a type-I band alignment. In contrast, in the SeMoS/g-C3N4 configuration, the two fields oppose each other, leading to a net electric field directed from MoSSe to g-C3N4 layer. This leads to a type-II band alignment, which facilitates spatial carrier separation and significantly enhances photocatalytic water-splitting activity. Furthermore, this study also demonstrates that biaxial strain can effectively modulate the electronic band structures of both types of heterostructures. In particular, the SeMoS/g-C3N4 system exhibits a reversible transition between type-I and type-II band alignments under specific compressive (–4%) and tensile (+5%) strain states. The underlying mechanism is elucidated by the difference charge density calculations. This study provides theoretical insights into the role of interfacial and intrinsic dipoles combined with strain engineering, offering a viable route for designing efficient MoSSe/g-C3N4-based photocatalysts and optoelectronic devices.
Numerical simulation of magnetism and magnetocaloric effect of Mn-rich Ni-Mn-Ga alloy
WANG Bo, ZHANG Yufen, SHAO Hui, ZHANG Zeyu, HU Yong
2026, 75 (1): 010707. doi: 10.7498/aps.75.20251394
Abstract +
This work investigates the magnetocaloric effect-based green magnetic refrigeration technology, with a focus on Ni-Mn-Ga Heusler alloy as a promising magnetic refrigerant candidate. To elucidate the role of Mn-rich composition in regulating the magnetic and magnetocaloric properties, a multi-scale computational approach integrating first-principles calculations and Monte Carlo simulations is adopted. This method enables a detailed analysis of how Mn atoms occupying Ni and Ga sites influence the microstructure, atomic magnetic moments, exchange interactions, and macroscopic magnetocaloric response of the alloy. The results indicate that Mn site occupancy critically affects the magnetic performance: the occupation of Ni sites reduces the total magnetic moment and Curie temperature, thereby reducing the magnetic entropy change; in contrast, Mn occupying Ga sites significantly enhances both the total magnetic moment and the magnetic entropy change. Notably, the Ni8Mn7Ga1 alloy achieves a maximum magnetic entropy change of 2.32 J·kg–1·K–1 under a 2 T magnetic field, which significantly exceeds that of the stoichiometric Ni8Mn4Ga4 alloy. Further electronic structure analysis reveals that Mn content variation modulates the density of states near the Fermi level and optimizes orbital hybridization and ferromagnetic exchange interactions, thus adjusting the magnetic phase transition behavior. Critical exponent analysis confirms that the magnetic interactions are inherently long-range and tend toward mean-field behavior with compositional changes. By establishing a clear “composition-structure-magnetism-magnetocaloric performance” relationship on an atomic scale, this work provides theoretical foundations for designing high-performance, low-hysteresis magnetic refrigeration materials.

EDITOR'S SUGGESTION

Technology for enhancing critical current of YBCO superconducting tapes via proton irradiation
ZHU Xiaofeng, ZHANG Suping, ZHANG Ning, ZHOU Hongji, WANG Chuan, PAN Gaofeng, LI Pengzhan, WANG Yang, ZHANG Tianjue
2026, 75 (1): 010803. doi: 10.7498/aps.75.20251031
Abstract +
This research adopts an innovative method, i.e. proton irradiation technology, for realizing defect control in practical engineering yttrium barium copper oxide (YBCO) tapes, in order to improve the critical current density of YBCO high-temperature superconducting tapes in high magnetic fields. Based on the material irradiation terminal of the 4.5 MV electrostatic accelerator at Peking University, systematic irradiation experiments are conducted using 3 MeV proton beams on YBCO superconducting tapes at different fluence rates, successfully constructing high-density, low-dimensional controllable artificial pinning centers in the high superconducting tapes. This defect engineering significantly suppresses the flux creep phenomenon and enhances the pinning effect by creating low-energy pinning sites for flux lines, thereby significantly weakening the inhibitory effect of external magnetic fields on critical current (Ic). Comparative analysis of superconducting tapes before and after irradiation is conducted, including superconducting transition temperature, superconducting critical performance, and dependence of critical current density on magnetic field. As the irradiation dose increases, high-density point defects (vacancies, interstitial atoms, etc.) and a small number of vacancy clusters are implanted inside the superconducting tape, resulting in a corresponding decrease in the superconducting phase. Therefore, as the dose increases, the orderliness of the superconducting phase in the superconducting tape decreases sharply, leading to a gradual widening of the superconducting transition temperature zone. By measuring the hysteresis loops of samples irradiated with different doses of protons and calculating the critical current density Jc based on the Bean model, the experimental data show that under irradiation conditions with a fluence rate of 8×1016 p/cm2, the critical current of the sample under extreme operating conditions of 4.2 K and 6.5 T achieves an 8-fold breakthrough improvement. Meanwhile, the maximum improvement factors in critical current density at 20 K and 5 T and 30 K and 4 T are also 5.5 times and 4.8 times, respectively. The logarithmic curve is fitted using the Jc ∝ B –α power exponent model, with the power parameter α values of 0.276, 0.361, and 0.397 for the variation of critical current density with magnetic field in three temperature ranges of 4.2 K, 20 K, and 30 K, respectively. This indicates that the superconducting tape irradiated with protons will form more effective strong pinning centers at lower temperatures, reducing the dependence of the critical current density of the superconducting tape on the magnetic field. This performance breakthrough significantly enhances the application potential of high superconducting tapes in low-temperature and high magnetic fields environments, especially in frontier fields such as particle accelerators and fusion reactors, where there is an urgent demand for high-performance superconducting magnets. This work confirms that the proton irradiation technology can efficiently optimize critical performance through defect engineering without changing the existing preparation process of YBCO tapes, thereby providing a highly feasible and process-compatible technical path for realizing the practical performance control of superconducting materials.

EDITOR'S SUGGESTION

Effects of helium concentration on defect evolution and mechanical properties in single-crystal iron: Laws and microscopic correlation mechanisms
WANG Lusheng, SHEN Liang, LUO Long, PENG Yanhong, YANG Guoping, ZHAO Han, DING Jun
2026, 75 (1): 010804. doi: 10.7498/aps.75.20251089
Abstract +
Understanding the intrinsic correlation between helium concentration and the evolution of defects as well as mechanical properties in low-activation steel on an atomic scale is crucial for designing fusion materials with excellent resistance to swelling and embrittlement. This study investigates the effect of helium concentration on single-crystal iron through molecular dynamics simulations, thereby clarifying the mechanisms by which helium concentration affects helium defect evolution, mechanical properties, and plastic deformation behavior of low-activation steel on an atomic scale. Models of body-centered cubic (BCC) iron with different helium concentrations (0.5%–4.5%) are established. Wigner-Seitz cell analysis and cluster clustering methods are employed to track the evolution of Frenkel Pairs (FPs) and cluster defects, revealing the mechanism of helium concentration-induced FPs and cluster formation at 500 ℃. Furthermore, combined with tensile mechanical simulations, the effects of helium behavior on the mechanical properties of single-crystal iron, such as elastic modulus, yield strength, and toughness, are analyzed, and the correlation mechanisms between helium concentration-induced defect evolution, mechanical properties, and plastic deformation behavior are revealed. The results show that when NHe < 3.0%, the number of FPs linearly reaches to a peak and then stabilizes. This is because helium behavior causes a rapid increase in the number of FPs and a large number of interstitial atoms are generated, some of which recombine. The annihilation rate of FPs increases with their number increasing and eventually equals the generation rate, resulting in a stable number of FPs. When NHe ≥ 3.0%, the initial increase and stabilization are the same as those for NHe < 3.0%. However, after the formation of large interstitial clusters, they absorb interstitial atoms and grow, hindering recombination and reducing the annihilation rate of FPs, thus leading to a secondary increase. The large clusters are surrounded by vacancies and no longer hinder FP recombination, and a new balance is achieved, resulting in a secondary stabilization of the FP number. When NHe increases to 3.0%, the elastic modulus, yield strength, and toughness of single-crystal iron decrease by 21%, 88%, and 57%, respectively; beyond this concentration, the mechanical properties no longer decrease. This is because when NHe < 3.0%, as helium concentration increases, helium-induced defects increase, leading to a decrease in toughness and promoting dislocation nucleation, thus reducing the elastic modulus and yield strength. When NHe ≥ 3.0%, dislocations exist in the initial defects, and the number of clusters changes slightly; toughness no longer decreases, and dislocation nucleation is not affected, leading to the stabilization of elastic modulus and yield strength. At NHe = 3.0%, the formation of large clusters hinders the movement of slip systems, changes the orientation of slip planes, weakens the effectiveness of the main slip system, which leads to an increase in small slip bands and causes the plastic deformation mechanism to transform from cross-slip to decomposition into discrete dislocations and point defects once the slip bands intersect with each other. This study reveals the influence patterns and key mechanisms of helium concentration on defect evolution and mechanical properties of single-crystal iron, providing a theoretical basis for designing fusion iron-based materials.
Emission performance at the interface of Zr/O/W Schottky thermal field emission cathodes
GUO Jiamei, YIN Shengyi, SUN Wanzhong, ZHANG Yongqing, JIN He, ZHAO Zichen
2026, 75 (1): 010805. doi: 10.7498/aps.75.20251100
Abstract +
The Zr/O/W Schottky-type thermal field emission cathode is a key component in advanced electron beam instrumentation, with its unique interfacial emission mechanism remaining a focus of research in cathode technology. Traditional understanding attributes the decrease of work function at the cathode tip to a monolayer adsorption of Zr-O dipoles on the W(100) facet, with the electropositive orientation directed outward, perpendicular to the surface. This study successfully fabricats a high-performance Zr/O/W Schottky-type thermal field emission cathode that exhibits exceptional emission characteristics, including a current density of 2.5×104 A/cm2 and operational stability exceeding 8000 h. Comprehensive microstructural characterization of the activated emission zone is performed utilizing energy-dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES), thereby precisely determining elemental distribution profiles across both surface and subsurface regions. The results reveal that during cathode preparation, the zirconia coating diffuses in the form of Zr-O complexes within the tungsten matrix, forming nanoscale enrichment zones specifically on the W(100) facet. Under operational conditions combining elevated temperature (1700–1800 K) and high electric field (>107 V/m), the W(100) surface develops not an adsorbed Zr-O dipole monolayer, but a nanoscale Zr/O/W(100) composite oxide structure. This multilayer structure consists of three coherently integrated components: 1) an oxygen-enriched diffusion layer beneath the W(100) interface, 2) the crystalline W(100) substrate, and 3) an overlying Zr-O thin film with multiatomic-layer thickness. First-principles calculations simulating the dynamic evolution of the W(100) emission interface during thermal treatment corroborate the experimental findings. The computed work function of the cathode emission surface decreases significantly from 5.02 eV (characteristic of nano-WO3) to 2.85 eV, showing excellent agreement with experimental measurements. When the emission interface becomes unbalanced due to external perturbations, the continuous diffusion of the zirconia coating toward the tip region, combined with the diffusion of Zr-O complexes from the subsurface of the W(100) crystal plane to the interface, enables autonomous replenishment of surface-active sites. This dynamic process effectively maintains a stable low-work-function emission surface. Both theoretical and experimental evidence consistently demonstrate that the Zr/O/W(100) oxide film serves as the fundamental material basis for the exceptional emission current density, remarkable stability, and extended operational lifetime of Zr/O/W cathodes.

EDITOR'S SUGGESTION

Integration and applications of two-dimensional materials
YANG Gaochen, MA Chenlong, XU Langlang, SHI Wenhao, HUANG Xinyu, SUN Mingjun, BI Ming, HE Xiao, MENG Xiaohan, LYU Shengjie, LIN Weijia, HE Min, TONG Lei, YE Lei
2026, 75 (1): 010810. doi: 10.7498/aps.75.20251386
Abstract +
As Moore’s Law encounters limitations in scaling device physical dimensions and reducing computational power consumption, traditional silicon-based integrated circuit (IC) technologies, which have enjoyed half a century of success, are facing unprecedented challenges. These limitations are especially apparent in emerging fields such as artificial intelligence, big data processing, and high-performance computing, where the demand for computational power and energy efficiency is growing. Therefore, the exploration of novel materials and hardware architectures is crucial to address these challenges. Two-dimensional (2D) materials have become ideal candidates for the next-generation electronic devices and integrated circuits (ICs) due to their unique physical properties such as the absence of dangling bonds, high carrier mobility, tunable band gaps, and high photonic responses. Notably, 2D materials such as graphene, transition metal dichalcogenides (TMDs), and hexagonal boron nitride (h-BN) have demonstrated immense potential in electronics, optoelectronics, and flexible sensing applications.This paper comprehensively reviews the recent advancements in the application of 2D materials in integrated circuits, analyzing the challenges and solutions related to large-scale integration, device design, functional circuit modules, and three-dimensional integration. Through a detailed examination of the basic properties of 2D materials, their constituent functional devices, and multifunctional integrated circuits, this paper presents a series of innovative ideas and methods, demonstrating the promising application prospects of 2D materials in future ICs.The research method involves a detailed analysis of the physical properties of common 2D materials such as graphene, TMDs, and h-BN, with typical application cases explored. This paper discusse how to utilize the excellent properties of these materials to fabricate high-performance single-function devices, integrated circuit modules, and 3D integrated chips, especially focusing on solving the challenges related to large-scale growth, device integration, and interface engineering of 2D materials. The comparison of the performance and applications between various materials demonstrates the unique advantages of 2D materials in the semiconductor industry and their potential in IC design.Although 2D materials perform well in laboratory environments, there are still significant challenges in practical applications, especially in large-scale production, device integration, and three-dimensional integration. Achieving high-quality, large-area growth of 2D materials, reducing interface defects, and improving device stability and reliability are still core issues that need to be addressed in research and industry. However, with the continuous advancements in 2D material fabrication technology and optimization of integration processes, these challenges are gradually being overcome, and the application prospects of 2D materials are expanding.

EDITOR'S SUGGESTION

Very-high-frequency magnetic core films for integrated volatage regulators
PENG Chuan, HE Yuhan, BAI Feiming
2026, 75 (1): 010706. doi: 10.7498/aps.75.20251372
Abstract +
With the rise and widespread applications of three-dimensional (3D) heterogeneous integration technology, inductive voltage regulators are becoming increasingly important for mobile terminals and high-computing-power devices, while also offering significant development opportunities for high-frequency soft magnetic films. According to the requirements of on-chip power inductors, we first review the advantages and limitations of three types of magnetic core films: permalloy, Co-based amorphous metal films, and FeCo-based nanogranular composite films, with a focus on the technical requirements and challenges of several μm-thick laminated magnetic core films. Secondly, almost all on-chip inductors are hard-axis excited, which means that the magnetic field of inductors should be parallel to the hard axis of the magnetic core. We thus compare the characteristics of two methods of preparing large-area films, i.e. applying an in-situ magnetic field and oblique sputtering, both of which can effectively induce in-plane uniaxial magnetic anisotropy (IPUMA). Their influences on the static and high-frequency soft magnetic properties are also compared. The influences of film patterning on the domain structures and high-frequency magnetic losses of magnetic cores, as well as corresponding countermeasures, are also briefly analyzed. Furthermore, the temperature stability of magnetic permeability and anisotropy of magnetic core films is discussed from the perspectives of process compatibility and long-term reliability. Although the Curie temperatures and crystallization temperatures of the three types of magnetic core films are relatively high, the upper limits of their actual process temperatures are affected by the thermal effects on the alignment of magnetic atomic pairs, microstructural defects, and grain size. Finally, the current bottlenecks in testing high-frequency and large-signal magnetic losses of magnetic core films are discussed, and potential technical approaches to achieving magnetic core films that meet the future demands of on-chip power inductors for higher saturation current and lower magnetic losses are outlined.

EDITOR'S SUGGESTION

First-principles study on catalytic mechanism of Li2O2 molecule oxidation reaction over defective graphene- supported Sm single-atom catalysts
XIAO Yu, KE Qiang, LEI Xueling
2026, 75 (1): 010301. doi: 10.7498/aps.75.20251108
Abstract +
Lithium-oxygen batteries (LOBs) are renowned for their ultrahigh theoretical energy densities. However, their practical applications are significantly limited by sluggish oxidation kinetics and elevated charge overpotentials. Most single-atom catalysts (SACs) utilized in LOBs are predominantly based on transition metals, which feature unsaturated d-orbital coordination. In contrast, the rare-earth element samarium (Sm) possesses a rich array of 4f-orbital electrons. Recent studies have demonstrated that Sm SACs can effectively enhance the conversion of polysulfides in lithium-sulfur batteries (LSBs) and achieve remarkable cycling stability in full-cell experiments. Inspired by the work, we systematically design and optimize 17 configurations of Sm SACs for LOBs by using first-principles calculations, which are denoted as SmNxCy (x + y = 4 or 6). Through comprehensive screening for stability and catalytic activity, we identify the SmN3C3-1 catalyst as an optimal candidate for LOBs. The catalytic mechanism of the SmN3C3-1 SAC over the oxygen evolution reaction of the Li2O2 molecule is investigated. The Gibbs free energy of the two-electron dissociation process indicates that the second step of the reaction is the rate-determining step (RDS). At the equilibrium potential, the charge overpotential is 0.52 V. Furthermore, mechanistic analysis reveals that the d-f-p orbital hybridization in SmN3C3-1 effectivelyreduces the shielding effect on the Sm 4f orbitals, facilitates interfacial charge transfer, and significantly improves the catalytic performance of the Li2O2 oxidation. This study provides novel insights into the potential of rare-earth-based SACs for improving the performance of LOBs.
Terahertz metasurface independently controlled by spatial vortex and spatiotemporal optical vortex
LI Yuxi, ZHANG Huiyun, CHEN Jiongxu, WANG Jiacheng, ZHANG Min, JIANG Qingyou, LIU Meng, ZHANG Yuping
2026, 75 (1): 010404. doi: 10.7498/aps.75.20251078
Abstract +
The optical vortex (OV) and spatiotemporal optical vortex (STOV) are special beams carrying different forms of orbital angular momentum (OAM). The OV has longitudinal OAM, whereas the STOV has transverse OAM and is coordinated with time to achieve control. Due to their reliance on different physical mechanisms, traditional optical platforms are difficult to independently control these two vortex beams on the same platform. This limitation, to some extent, hinders the understanding of the unified physical mechanism underlying spatial and spatiotemporal orbital angular momentum and also slows the development of multi-dimensional light field manipulation technology. This paper proposes a terahertz (THz) metasurface device based on vanadium dioxide (VO2) phase change material. The device integrates in-plane asymmetry, provided by triangular pores and required to excite STOV, with anisotropic phase units, realized by VO2 broken rings and needed to generate OV, into one metasurface platform, This integration enables dynamic switching of OV and STOV on the same metasurface platform. The uniqueness of its design and the key to achieving functional integration lie in the selection of Si and VO2 materials for the upper layer of the metasurface. When VO2 is in the insulating state, its dielectric constant in the THz band is similar to that of Si and its conductivity is very low. Different rotation angles of the units can still be considered as a periodic structure with the same symmetry on a macroscopic scale. The structure uses circularly polarized waves for reflection, generating a topological dark point at approximately 1.376 THz and a topological dark line between 1.3765 THz and 1.378 THz, which excites STOV. When VO2 transforms into a metallic state, its high conductivity makes the broken ring a dominant scatterer. By reasonably arranging the encoded units of the metasurface and combining the Pancharatnam-Berry (PB) phase, not only can OV with different topological charges be generated, but also multi-channel and multi-functional OV can be created through convolution theorem and shared aperture theorem. Subsequently, the influence of structural parameters is analyzed in detail. By changing the shape of the triangular pores and the thickness of the broken ring, the two vortex beams are adjusted, and it is found that they have strong topological stability under different conditions and can be reversibly switched through temperature control. This research provides a new idea for realizing multifunctional vortex light generation in the terahertz frequency band and opens up new avenues for the application of vortex light in terahertz communication and optical information processing.

EDITOR'S SUGGESTION

Metal contamination in process line of superconducting quantum processor chips
XU Xiao, ZHANG Haibin, SU Feifan, YAN Kai, RONG Hao, DENG Hui, YANG Xinying, MA Xiaoteng, DONG Xue, WANG Qiming, LIU Jialin, LI Manman
2026, 75 (1): 010601. doi: 10.7498/aps.75.20251101
Abstract +
The manufacturing process of superconducting quantum processor chips faces special challenges of metal contamination, and their material system and process characteristics are significantly different from those of traditional semiconductor chips. This study focuses on the issue of metal contamination in the fabrication process of quantum chips, systematically analyzing the sources, diffusion mechanisms, and prevention strategies of metal contamination in quantum chips, where the bulk diffusion and surface migration behaviors of superconducting materials (such as Ta, Nb, Al, TiN) on sapphire and silicon substrates are particularly emphasized, aiming to provide theoretical basis and technical references for process optimization and to promote the industrialization process of quantum computing technology.The metal contamination in the fabrication of quantum chips is mainly caused by the metal film materials used in the process, the external environment, or the unintended metal impurity atoms introduced in the manufacturing process. Among them, some quantum chip components directly use superconducting metal materials. Unlike semiconductor chips, they cannot achieve front and back stage isolation, resulting in the continuous presence of metal surface migration channels, and the exposed metal structures on the chip surface. Metal contamination often leads to two basic failure problems: short circuits and leakage currents. These problems mainly result from the bulk diffusion of metal impurities in the dielectric layer and the migration behavior on the sample surface. The diffusion and migration rates of metals are affected by temperature, interface reactions, defects, and grain boundaries. The results show that the sapphire substrate, due to its dense lattice structure, exhibits excellent anti-diffusion performance, reducing the risk of contamination and providing a stable interface environment for superconducting quantum chips. For silicon substrates, special attention must be paid to the contamination risks from high-mobility metals such as Au, In, and Sn. Experimental verification shows that Ti/Au under bump metallization structures on silicon substrates are prone to Au penetration diffusion, and increasing Ti thickness does not significantly improve the blocking effect. The low-temperature process (< 250 ℃) and ultra-low-temperature operating environment (mK level) of quantum chips effectively suppress metal diffusion, but the exposed metal surfaces and material diversity still pose unique challenges.The study recommends establishing a dedicated metal contamination prevention system for quantum chips and proposes future research directions, including the evaluations of novel materials, surface state regulation, and long-term reliability studies. This work provides important theoretical support and technical guidance for optimizing the process and enhancing the performance of superconducting quantum chips.
Spatial attitude optimisation of three-dimensional cold mass support system for superconducting magnets for vehicular transport environments
ZHENG Yichuan, XU Ce, WANG Hui, CHEN Shunzhong, CHENG Junsheng, WANG Qiuliang
2026, 75 (1): 010801. doi: 10.7498/aps.75.20250894
Abstract +
The spatial attitude and dynamic performance of the cold mass support system for superconducting magnets are critical for engineering applications. This study aims to develop a design method for the spatial attitude of tie rods through a series of theoretical derivations and simulations, enabling superconducting magnets to possess a certain degree of dynamic environmental adaptability. This paper first constructs a mathematical model of the three-dimensional cold mass support system under impact loads. Stress formulas for the tie rod under vertical 5g, axial 3g, and lateral 3g impact loads are derived. Based on this, a penalty term for stress differences is introduced to construct the objective function, and the spatial inclination angle of the tie rod is optimised. After determining the acute angle between the tie rod and the coordinate axis, the cold mass support structure exhibits four different attitudes. In order to keep the natural frequency of the magnet away from the main excitation frequency band of vehicle transportation, this study uses the finite element method to perform modal analysis and proposes a method for posture design based on the principle of maximising the first-order natural frequency. Finally, random vibration simulations are conducted for the vibration environment of highway transportation. Reference points are established at both ends of the axis of the magnet body components and the room-temperature tube axis. The displacement response power spectral density (PSD) curves and root mean square values of the reference points during vibration are analysed. The conclusions of this study are as follows. 1) When the acute angles α, β, and γ included between the tie rod and the vertical, axial, and lateral directions are 31.22°, 68.50°, and 68.50°, respectively, the mechanical performance of the three-dimensional cold mass support system reaches its optimal state. 2) When the tie rod is installed in the spatial attitude configuration, the first-order natural frequency of the cold mass system is the highest, with a value of 125.99 Hz. 3) During long-distance integrated vehicle transportation, the maximum values of the vertical and lateral displacements of the magnet assembly axis relative to the room-temperature tube axis are both less than 0.1 mm. The maximum stress locations are both at the root of the carbon fibre tie rod, far below the strength limit of carbon fibre composite materials, indicating that the superconducting magnet possesses a certain degree of dynamic environmental adaptability. These analysis results provide theoretical guidance and data support for the structural safety and stability of this type of superconducting magnet during long-distance integrated vehicle transportation.
Influence of micro-alloying element La on solidification microstructure of Al-Mg alloy inoculated with Al-5Ti-1B
LI Ciyu, ZHANG Lili, ZHANG Yue, JIANG Hongxiang, ZHAO Jiuzhou, HE Jie
2026, 75 (1): 010806. doi: 10.7498/aps.75.20251122
Abstract +
Grain refinement is an effective method to enhance the comprehensive properties of alloys. In industrial production, Al-5Ti-1B master alloys are commonly used to refine the microstructure of aluminum alloys. However, the grain refinement potency of Al-Ti-B master alloys is limited and cannot meet the requirements for high-performance aluminum alloy applications. It has been demonstrated that adding trace amount of micro-alloying element La to the aluminum alloy melt inoculated with Al-5Ti-1B master alloy can further refine the solidification microstructure. Previous research indicates that the addition of 0.06% (weight percent) La is sufficient to achieve an ideal α-Al grain refinement. Our recent experimental results demonstrate that for an Al-Mg alloy of high Mg content inoculated with Al-5Ti-1B master alloy, the optimal addition level of La is about 0.02% (weight percent).Solidification experiments are carried out for Al-Mg alloys inoculated with Al-5Ti-1B master alloy and different addition levels of micro-alloying element La. It is demonstrated that the trace addition of micro-alloying element La shows a further grain refinement effect on Al-Mg alloy and reduces the nucleation undercooling of α-Al. A model is proposed for the segregation behavior of micro-alloying element La at the interface between the Al alloy melt and TiB2. The mechanism of the enhancement in the efficiency of TiB2 particles to nucleate α-Al by micro-alloying element La is clarified. The calculation results indicate that La shows a strong segregation tendency toward the interface between the Al melt and TiB2 particles, thus reducing the interfacial energy and contact angle between TiB2 and α-Al, enhancing the efficiency of TiB2 to nucleate α-Al, and further refining α-Al grains.
Review

EDITOR'S SUGGESTION

Research progress of robust magnetic resonance wireless power transfer based on topological physics
WU Xian, HUANG Youtao, LI Hui, YANG Yaping, CHEN Hong, GUO Zhiwei
2026, 75 (1): 010701. doi: 10.7498/aps.75.20250833
Abstract +
Magnetic resonance wireless power transfer (WPT) has gradually become a popular research topic of near-field regulation in recent years, with wide applications in the fields of mobile phones, implantable medical devices, electric vehicles, and many other fields. However, several challenges remain to be addressed: near-field coupling, which induces multiple frequency splits and prevents the system from maintaining a fixed operating frequency; coupled arrays, which are susceptible to structural errors and parameter perturbations; current research, which primarily focuses on single-load transmission and has resulted in undeveloped multi-load transmission systems; the direction of transmission, which is difficult to control flexibly. In recent years, photonic artificial microstructures have provided a flexible platform for studying topological physics, arousing significant research interest in their fundamental topological characteristics. The most prominent features of topological structures are their nonzero topological invariant and the robust edge states determined by the bulk-edge correspondence: these features can overcome disturbances caused by defects and disorders. Moreover, by modulating the wave function distribution of topological states, energy can be precisely localized, enabling directional WPT. Therefore, implementing topological modes in WPT systems are of significant scientific importance.This review summarizes recent researches on topological models for robust WPT, which are divided into three main parts. The first part introduces one-dimensional periodic topological structures, focusing primarily on the significant improvements in transmission efficiency and robustness achieved by utilizing topological edge states in the Su-Schrieffer-Heeger (SSH) model for WPT. Moreover, a composite chain formed by two SSH chains is constructed to realize a higher-order parity-time (PT) symmetric topological model. This approach solves the frequency splitting caused by coupled edge states and exhibits lower power losses in standby mode. The second part discusses several types of aperiodic one-dimensional topological chains. By introducing topological defect states at the interface between two different dimer chains, robust multi-load WPT is achieved. Furthermore, based on the integration of artificial intelligence algorithms, the SSH-like topological model enables more efficient and robust WPT than traditional SSH model. The asymmetric edge states in quasi-periodic Harper chain provide a solution for directional transmission in WPT applications. By introducing nonlinear circuits, this model enables active control of the transfer direction. The third part presents the application of high-order topological corner states in multi-load robust WPT, demonstrating the selective excitation of both symmetric and asymmetric corner modes.Finally, the application prospects of topological modes in WPT systems are discussed. With the development of new physics, the integration of non-Hermitian physics and topological physics holds great promise for achieving simultaneous energy-information transfer, and is expected to achieve compatible WPT, wireless communication, and wireless sensing within a single system. Such a fusion technology will provide breakthroughs in efficiency, robustness, and multifunctionality for next-generation wireless systems.

EDITOR'S SUGGESTION

Research progress of Al1–xScxN ferroelectric thin films
ZHAO Yongsong, ZHOU Dayu, TONG Yi, WANG Xinpeng, QIN Haiming
2026, 75 (1): 010808. doi: 10.7498/aps.75.20251241
Abstract +
Al1–xScxN, as a new generation of wurtzite-type ferroelectric material, has become a focal point in ferroelectric materials research in recent years, due to its high remnant polarization, nearly ideal rectangular polarization-electric field hysteresis loops, inherent compatibility with back-end-of-line (BEOL) CMOS processes, and stable ferroelectric phase structure. The systematic and in-depth studies on the preparation, property modulation, and device applications of this material have been conducted. This paper provides a comprehensive review of the research progress of Al1–xScxN ferroelectric thin films. Regarding the factors influencing ferroelectric properties, it emphasizes the regulatory effects of Sc doping concentration on phase transition and coercive field, explores the influences of substrate (such as Si and Al2O3) and bottom electrode (such as Pt, Mo, and HfN0.4) on thin-film orientation, stress, and interface quality, and systematically summarizes the influences of deposition conditions, film thickness, testing frequency, and temperature on ferroelectric performance. At the level of physical mechanisms governing polarization switching, this review elaborates on the domain structure, domain wall motion dynamics, nucleation sites and growth mechanisms in the Al1–xScxN switching process, revealing its microscopic response behavior under external electric fields and the mechanisms underlying fatigue failure. In terms of application prospects, Al1–xScxN thin films show significant advantages in memory devices such as ferroelectric random-access memory (FeRAM), ferroelectric field-effect transistors (FeFETs), and ferroelectric tunnel junctions (FTJs). Their high performance and integration compatibility provide strong technical support for developing next-generation, high-density, low-power ferroelectric memory and nanoelectronic devices.
GENERAL
Analysis of dynamics and energy consumption in capacitor-free memristive neural circuit
GUO Qun, XU Ying
2026, 75 (1): 010001. doi: 10.7498/aps.75.20251114
Abstract +
To address the issues of high dynamic power consumption and substantial occupation of silicon integration resources in traditional capacitor-containing neuronal circuits, this study proposes a capacitor-free neuronal circuit based on a charge-controlled memristor. By taking the intrinsic parameters of the charge-controlled memristor as the reference for scaling transformation, dimensionless dynamical equations are derived. The local asymptotic stability of the system is verified using Jacobian matrix eigenvalue decomposition and the Routh-Hurwitz criterion. Gaussian white noise is introduced to simulate the interference for detecting coherent resonance, while energy characteristics are analyzed by combining Hamiltonian energy formulas and resistance energy consumption expressions. Additionally, the fourth-order Runge-Kutta method is adopted to conduct numerical simulations.The research results indicate that external stimulus, ionic channel conductance, and reversal potential can flexibly regulate the periodic/chaotic firing modes of the neuron. In the periodic state, the proportion of electric field energy of the charge-controlled memristor in the total energy is higher; in the chaotic state, however, the proportion of magnetic field energy of the inductive coils increases. The circuit exhibits coherent resonance under the influence of noise, and resistor is the main energy-consuming component. The conclusion proves that the circuit is feasible in principle, with rich dynamical characteristics and good noise robustness. Adjusting the resistance value can enhance energy efficiency while preserving multiple firing modes, thereby providing theoretical support and optimization direction for designing high-integration, low-power neuromorphic computing circuits.
Bonder collision bifurcations and co-dimensional bifurcations in a class of Piecewise-Smooth discontinuous mappings
DENG Haozhou, WANG Like, ZHU Zhaorui, WANG Hengtong, QU Shixian
2026, 75 (1): 010002. doi: 10.7498/aps.75.20251167
Abstract +
The study of chaos is an important field in science and has achieved many significant results. In the earlier days of the field, the study mainly focused on the systems that exhibit smooth behaviors throughout. Nonsmooth systems, by contrast, have received less attention. Nonsmooth dynamical systems are widely encountered in practical applications, such as impact oscillators, relaxation oscillators, switch circuits, neuron firing, epidemic models, and even economic models. They have become an active field of study in recent years. The typical characteristics of those systems are the abrupt variation of dynamics following a slow evolution over a longer period of time. Piecewise smooth maps are important models frequently used to describe the dynamics of those systems. Among them, much attention is paid to a class of generally one dimensional piecewise linear discontinuous mappings, as they are easy to handle and can display a rich variety of dynamical phenomena with new characteristics.Included in this work is a discontinuous two-piece mapping function. The left branch is a linear function with slope α, and the right branch is a power law function with exponent z. There exists a gap limited by $[\mu,\mu+\delta]$ at $x=0$, where μ is the control parameter and δ is the width of the gap. Even though the dynamics of nonsmooth and continuous mapping have been extensively studied at some special z values, their discontinuous counterparts have not been investigated at any z and discontinuous gap δ. The presence of a discontinuity may induce border collision bifurcations. The interplay between these bifurcations associated with stability analysis and the border collision bifurcations may produce complex dynamics with new characteristics. Therefore, this work investigates the dynamics of those mappings in which periodic increments, periodic adding and coexistence of attractors are observed. The border collision bifurcation often disrupts a stable periodic orbit, causing it transition into either a chaotic state or a different periodic orbit. Near the critical parameters of this bifurcation, a periodic orbit often coexists with a chaotic or another periodic attractor. A general approach is proposed to analytically and numerically calculate the critical control parameters at which the border collision bifurcations happen, which transform the problem into the solution of an algebraic equation of dimensionless control parameter μ/μ0, where μ0 is the critical control parameter when δ = 0. The solution can be obtained analytically when z is a simple rational number or small integer, and numerically for an arbitrary real number. In this way, the stability condition and critical control parameters for the periodic orbit of type $L^{n-1}R $ are analytically or numerically obtained under the arbitrary exponent z and discontinuous gap δ. The results are in accordance with the numerical simulations very well. Based on the stability and border collision bifurcation analysis, the phase diagrams in the plane of two dimensional parameters μ−δ are built for different ranges of z. Their dynamical behaviors are discussed, and three types of co-dimension-2 bifurcations are observed, and the general expressions for the coordinates at which those phenomena occur are obtained in the phase plane. Meanwhile, a specular tripe-point induced by merging of co-dimension-2 bifurcation points BC−-flip and BC−-BC− is observed in the phase plane, and the condition for its existence is analytical obtained.
Discrete memristor-based complex-valued chaotic system dynamic analysis and its application in dual-image encryption
DENG Quanli, WANG Chunhua, YANG Gang
2026, 75 (1): 010003. doi: 10.7498/aps.75.20251242
Abstract +
The exploration of complex-valued chaos not only provides a feasible approach for practical applications such as image encryption, but also has great potential in simulating wave phenomena and quantum inspired process. In order to bridge it with nonlinear circuit components, we introduce a novel complex-valued chaotic system by embedding a discrete memristor into a complex Gaussian map. The memristor, a component with inherent physical memory, is uniquely driven by the modulus of the complex state variable, which is a key physical quantity often related to energy or amplitude in wave systems. This coupling induces complex nonlinear dynamics, which are physically characterized through Lyapunov exponents and bifurcation analysis, revealing an enhanced and more robust chaotic regime. The physical feasibility of this system is demonstrated by its successful hardware realization on an FPGA platform. To demonstrate its potential applications, we leverage the complex chaotic flows of the system to engineer a dual-image encryption scheme, where the encryption process is explained as a physical diffusion and scrambling of information represented by a complex matrix. Our results verify that this approach not only yields a cryptosystem with high security but also provides a link between complex chaos and information security applications.
Dual-paramter-scanning-based quantum- memory- assisted measurement-device-independent quantum key distribution protocol
LIU Chang, SUN Mingshuo, LUO Yizhen, DONG Shuyan, ZHANG Chunhui, WANG Qin
2026, 75 (1): 010602. doi: 10.7498/aps.75.20251171
Abstract +
Measurement-device-independent quantum key distribution (MDI-QKD) protocol can effectively resist all possible attacks targeting the measurement devices in a quantum key distribution (QKD) system, thus exhibiting high security. However, due to the protocol’s high sensitivity to channel attenuation, its key generation rate and transmission distance are significantly limited in practical applications.To improve the performance of MDI-QKD, researchers have proposed quantum-memory (QM)-assisted MDI-QKD protocol, which has enhanced the protocol's performance to a certain extent. Nevertheless, under finite-size conditions where the total number of transmitted pulses is limited, accurately estimating the relevant statistical parameters is still a challenge. As a result, existing QM-assisted MDI-QKD schemes still encounters issues such as low key rates and limited secure transmission distances.To solve these problems, this work proposes a novel improved finite-size QM-assisted MDI-QKD protocol. By utilizing quantum memories to temporarily store early-arriving pulses and release them synchronously, the protocol effectively reduces the influence caused by channel asymmetry. Additionally, the protocol introduces a four-intensity decoy-state method to improve the estimation accuracy of single-photon components. Meanwhile, to mitigate the influence of finite-length effects on QM schemes, the proposed protocol combines a collective constraint model and a double-scanning algorithm to jointly estimate scanning error counts and vacuum-related counts. This approach enhances the estimation accuracy of the single-photon detection rate and phase error rate under finite-size conditions, thereby significantly improving the secure key rate of the MDI-QKD system.Simulation results show that under the same experimental conditions, compared with the existing QM-assisted three-intensity decoy-state MDI-QKD protocol and the four-intensity decoy-state MDI-QKD protocol based on Heralded Single-photon Source (HSPS), the proposed protocol extends the secure transmission distance by more than 30 km and 100 km, respectively. This proves that under the same parameter settings, the proposed scheme exhibits significant advantages in both key rate and secure transmission distance. Therefore, this research provides important theoretical references and valuable benchmarks for developing long-distance, high-security quantum communication networks.

EDITOR'S SUGGESTION

Asymmetric gear driven by Brownian particles with non-reciprocal interactions
WANG Yan, LI Jiajian, AI Baoquan
2026, 75 (1): 010901. doi: 10.7498/aps.75.20251168
Abstract +
In this work, we use computer simulations to examine how an asymmetric gear can be driven by Brownian particles that interact in a non-reciprocal manner. Unlike many active matter systems, the particles are not self-propelled. Instead, the non-reciprocal interactions break action-reaction symmetry and produce a net force that drives the system out of equilibrium. The gear has an asymmetric shape, which helps select a preferred direction of rotation.We find that the rotation direction of the gear is influenced by both the asymmetry and parameters of system. When system parameters are identical, gears with two structures of opposite chirality exhibit equal magnitudes of average angular velocity, differing only in their rotational directions. For a specific gear, the rotation speed increases as the strength of the non-reciprocal interaction increases and shows non-monotonic dependence on temperature and particle density. Interestingly, under high density conditions, the rotation direction can reverse. At low temperatures, particle clusters form, resulting in reversed motion, whereas higher temperatures restore the rotation in the original direction.This work illustrates how non-reciprocal interactions can be used to generate directed motion in passive structures such as gears. It offers one possible approach to controlling motion in small-scale systems without external energy input, and may contribute to the design of simple nanoscale machines.
ATOMIC AND MOLECULAR PHYSICS

EDITOR'S SUGGESTION

Electron impact ionization of C, N, and O at boundary of solar radiation/convection zone
HOU Yong, LUO Qingbo, LIANG Xin, ZENG Jiaolong, YUAN Jianmin
2026, 75 (1): 010302. doi: 10.7498/aps.75.20251144
Abstract +
The solar radiation-convection boundary ($ T \thicksim 180$ eV, $ n_{\mathrm{e}} \thicksim 9 \times 10^{22}\;{\rm{cm}}^{-3}$) marks the transition from radiative to convective energy transport, serving as a natural laboratory for hot dense plasmas. Its physical properties are crucial for stellar evolution and energy transport models, yet how electron-impact ionization (EII) is influenced by hot-dense environment effects—such as electron screening and ion correlation—remains unclear. To address this, we systematically calculate EII cross sections for C, N, and O ions under realistic solar boundary conditions, focusing on the role of environmental effects. We develop a novel computational framework that integrates hot-dense environment effects into atomic structure calculations: the Flexible Atomic Code (FAC) for atomic structure is combined with the Hypernetted-chain (HNC) approximation to capture electron–electron, electron–ion and ion-ion correlations, enabling self-consistent treatment of electron screening and ion correlation. Atomic wave functions are derived by solving the Dirac equation within the ion-sphere model, using a modified central potential that combines both free-electron screening and ion–ion interactions. EII cross sections are then computed via the distorted-wave (DW) approximation in FAC. The results demonstrate that the hot-dense environment effects significantly enhance the electron-impact ionization cross sections of C, N, and O, compared with those calculated under the free-atom model. Additionally, a notable reduction in the ionization threshold energy is observed. These effects are attributed to the overlap of atomic potentials due to strong ion coupling and the shift in bound-state energy levels caused by free-electron screening. For instance, under solar boundary conditions, the ionization cross section of C+ is increased by up to 50%, with the ionization threshold decreasing from about 24 eV (isolated) to 18 eV (with screening). Similar enhancements are observed for nitrogen and oxygen ions across various charge states. By establishing updated ionization cross sections for C, N, and O ions under realistic solar interior conditions, this work provides fundamental parameters for improving radiation transport models, ionization balance calculations, and equation-of-state models in stellar interiors. The results underscore the necessity of incorporating hot-dense environment effects in the calculations of atomic processes in hot dense plasmas, which is of great significance for astrophysics and inertial confinement fusion research.

EDITOR'S SUGGESTION

Internuclear-distance dependence of photoionization time delay in CO molecules
BAI Guangru, REN Zhongxue, ZHANG Bin, YANG Yan, LANG Yue, LIU Jinlei, ZHAO Jing, ZHAO Zengxiu
2026, 75 (1): 010303. doi: 10.7498/aps.75.20251234
Abstract +
Photoionization time delay in atoms and molecules is a fundamental phenomenon in attosecond physics, encoding essential information about electronic structure and dynamics. Compared with atoms, molecules exhibit anisotropic potentials and additional nuclear degrees of freedom, which renders the explanation of molecular photoionization time delays more complicated but also more informative. In this work, we investigate the dependence of the photoionization time delay on the internuclear distance in the 5σ→kσ ionization channel of carbon monoxide (CO) molecules. The molecular ground state is obtained using the Hartree-Fock method, and the photoionization process is treated within quantum scattering theory based on the iterative Schwinger variational principle of the Lippmann-Schwinger equation. Numerical calculations are performed with the ePolyScat program to obtain molecular-frame differential photoionization cross sections and time delays at various internuclear distances. Our results show that the extrema of the photoionization time delay occur near the peaks and dips of the differential cross section and shift toward lower energies as the internuclear distance R increases. At low energies, the time delay at the O end increases with R, while it decreases at the C end. This behavior is attributed to the asymmetric charge distribution and the resulting short-range potential difference between the two atomic sites. Around the shape-resonance energy region, both cross section and time delay display pronounced peaks associated with an l = 3 quasi-bound state. As R increases, the effective potential barrier broadens, the quasi-bound state energy moves toward lower values, and its lifetime becomes longer, leading to enhanced resonance amplitude and increased time delay. In the high-energy region, opposite-sign peaks of time delay are found along the O and C directions, corresponding to minima in the cross section. These features are well explained by a two-center interference model, where increasing R shifts the interference minima and the associated time-delay peaks toward lower energies. This study provides deeper insights into the photoionization dynamics of CO molecules, explains the role of nuclear motion, and provides valuable references for studying the photoelectron dynamics of more complex molecular systems.
ELECTROMAGNETISM, OPTICS, ACOUSTICS, HEAT TRANSFER, CLASSICAL MECHANICS, AND FLUID DYNAMICS
Orbital angular momentum pattern recognition method for vortex beam superposition states based on convolutional neural network and improved vision transformer
SONG Zekun, LIU Tao, ZHAO Zhenbing, ZHANG Rongxiang, DAI Huade
2026, 75 (1): 010402. doi: 10.7498/aps.75.20251048
Abstract +
This work proposes a pattern recognition method for the superposition state orbital angular momentum (OAM) of vortex beams based on convolutional neural network (CNN) and improved vision transformer (VIT). Organically integrating the local feature extraction advantages of CNN with the global fast classification ability of VIT driven by sparse attention mechanism, using three sets of Laguerre-Gaussian (LG) beam patterns with superimposed light field intensity distribution maps of ocean turbulence distortion as input, efficient and accurate recognition of end-to-end wavefront distortion is realized. MATLAB numerical simulation is adopted to simulate the superposition state LG beam in ocean turbulent environment, power spectrum inversion method is used to simulate ocean turbulence, and recognition accuracy and confusion matrix are used as evaluation indicators for OAM pattern recognition. The experimental results show that the CNN-VIT model exhibits excellent performance in OAM pattern recognition accuracy under different ocean turbulence intensities, wavelengths, transmission distances, and mode intervals. Compared with existing CNN and VIT, the proposed model improves recognition accuracy by 23.5% and 9.65% respectively under strong ocean turbulence conditions, thus exhibiting strong generalization ability under unknown ocean turbulence strengths. This demonstrates the potential application of the CNN-VIT model in OAM pattern recognition of vortex light superposition states.
Simulation design of reconfigurable microwave photonic channelized receiver based on coupled-resonator optical waveguide filter array
FAN Yan, LI Liu, GUO Zhengyu, WANG Haoran, XIONG Ziyang, DENG Hao, LIN Tong, LYU Junpeng, NI Zhenhua
2026, 75 (1): 010403. doi: 10.7498/aps.75.20251074
Abstract +
To meet the growing demand for high-frequency broadband signal processing in complex electromagnetic environments and to overcome the limitations of traditional electronic systems such as restricted bandwidth, limited response speed, and low integration density, this paper presents a reconfigurable microwave photonic channelized receiver chip implemented on a silicon photonic platform. The proposed architecture adopts a two-stage optical filtering strategy that circumvents the typical strict wavelength alignment requirements in traditional designs, thereby greatly alleviating the challenges of system integration. In the first stage, the cascaded Mach-Zehnder interferometer (MZI)-based wavelength division multiplexers (WDMs) are used to perform Gaussian-shaped filtering of the input optical spectrum with a channel spacing of approximately 200 GHz. The second stage combines an array of coupled resonator optical waveguide (CROW) filters functioning as finely tunable bandpass elements. These CROW filters utilize curved waveguide directional couplers, which are specifically designed to address the issues found in traditional multimode interference (MMI) couplers such as high insertion loss—and in straight directional couplers, which encounter significant coupling dispersion. The optimized curved coupler exhibits an insertion loss below 0.03 dB and a coupling ratio variation of less than 10% across the 1500–1600 nm wavelength band. Filter bandwidth reconfigurability is achieved via thermo-optic tuning of the balanced MZI embedded within each CROW filter, enabling dynamic adjustment of the coupling coefficients. Each filter exhibits a continuously adjustable 3 dB bandwidth ranging from 2.25 GHz to 3.12 GHz, with an excellent 20 dB/3 dB shape factor of 3.08. This performance indicates significantly improved roll-off characteristics compared with the performance of traditional filter designs, leading to enhanced suppression of image frequency components and improved signal separation fidelity.A complete microwave photon channelized receiving link is constructed using an integrated WDM-CROW filter bank. System-level simulations confirm that the architecture provides excellent broadband adaptability, supporting the channelization of radio frequency (RF) signals in two operational bands: 8–28 GHz and 8–36 GHz. The system efficiently decomposes the input wideband RF signal into eight independent intermediate frequency (IF) sub-bands. Within each sub-band, an image rejection ratio (IRR) exceeding 22 dB is maintained. The corresponding IF ranges are 1.4–3.6 GHz when configured for 8–28 GHz RF input, and 2–5 GHz for 8–36 GHz input, covering critical communication and detection bands from X-band to K-band and satisfying the requirements of multi-scenario signal processing. Furthermore, we simulate the reception and reconstruction of a 5 GHz bandwidth linear frequency-modulated (LFM) signal, successfully verifying the chip’s capability in handling wideband waveforms. These results underscore the feasibility of the proposed chip as a high-performance solution for advanced applications such as radar detection and broadband electronic warfare systems, offering a novel, integrated photonic alternative to traditional channelized reception architectures.

EDITOR'S SUGGESTION

Numerical analysis and optimization of high-efficiency 2.8 μm erbium-doped fluoride fiber laser based on dual-wavelength pump
LI Shuangjiang, ZHAO Hongru, FU Shijie, ZHANG Junxiang, ZHANG Lu, YAO Zhidong, SHENG Quan, SHI Wei, YAO Jianquan
2026, 75 (1): 010405. doi: 10.7498/aps.75.20251211
Abstract +
Er3+-doped ZBLAN fiber lasers have been widely investigated for generating high-power high-efficiency 2.8 μm mid-infrared lasers. High-power multimode 980 nm semiconductors are generally used as convenient pump sources in Er3+-doped ZBLAN fiber lasers. However, the longer lifetime of the lower laser level (4I13/2, 9.9 ms) than that of the upper laser level (4I11/2, 6.9 ms) results in severe self-terminating transition. Although highly Er-doped fibers with improved energy transfer upconversion rates can alleviate this problem to some extent, there are still significant limitations in heat load management. On the other hand, the 1.6–1.7 μm laser is used as another pumpscheme due to the partial spectral overlap between ground state absorption (GSA) and excited state absorption (ESA) for population inversion. This pump scheme demonstrates a slope efficiency of up to 50%. However, due to the weak GSA process, a 10 m-long active fiber is required. To address this issue, we propose a dual-wavelength (1.5 μm and 1.7 μm) pumping technique to achieve high-efficiency 2.8 μm laser output by using an Er3+-doped ZBLAN fiber with meter-level length. A simulation model is established for the dual-wavelength pumping scheme. This scheme combines the strong GSA process in the 1.5 μm band and the strong ESA process in the 1.7 μm band to accelerate the population accumulation on the lower laser level, promote the absorption of the 1.7 μm pump, and thereafter enable the conversion to 2.8 μm laser over much shorter gain fiber. By considering the intensities of ground state absorption and emission of the 4I15/2→4I13/2 transition, the pump at 1470 nm is selected to efficiently populate the Er3+ to the lower laser level. Then the second pump is optimized to a wavelength of 1680 nm to achieve rapid particle extraction from the lower laser level, thereby realizing population inversion for efficient 2.8 μm laser generation over a meter-long gain fiber. Using the optimized pump wavelengths, the simulation of a 2.8 μm fiber laser based on a 0.5 m-long 0.015 mol/mol erbium-doped fluoride fiber shows that when a 20 W 1680 nm laser is used as the main pump source, only a 1.2 W 1470 nm auxiliary pump is required to achieve a 12.2 W 2.8 μm laser output, with an optical efficiency as high as 58.2%. Furthermore, the fiber laser simulation indicates that when the powers of the two pumps satisfy the relationship of Pλ2 = 20Pλ1 – 4, the output power of the laser system can reach its maximum value. The dual-wavelength pumping technique proposed in this work enables high-efficiency 2.8 μm mid-infrared laser generation by using meter-long Er3+-doped fluoride fiber, which significantly improves the laser system integration and economic benefits.
Numerical simulation of three-phase Rayleigh-Taylor instability based on phase field model using lattice Boltzmann method
YANG Xuguang, WANG Xin, YUAN Xiaolei
2026, 75 (1): 011001. doi: 10.7498/aps.75.20251095
Abstract +
This paper develops a regularized lattice Boltzmann method for efficiently simulating the flow of N-phase immiscible incompressible fluids based on the phase field model that satisfies conservation and compatibility. By designing auxiliary moments, this method can accurately recover the second-order Allen-Cahn equation and the modified momentum equation. The correctness and effectiveness of the developed N-phase regularized lattice Boltzmann method are validated through numerical simulations of three-phase liquid lens spreading and Kelvin-Helmholtz instability phenomena. Finally, numerical simulations and analyses of three-phase Rayleigh-Taylor instabilities (RTI) are conducted, focusing on the evolution of the phase interface within the Reynolds number range of $ 500 \leqslant Re \leqslant 20000 $ (particularly under high Reynolds number condition of $ Re = 20000 $). Quantitative analyses are performed on the amplitude variations of bubbles and spikes at the two interfaces, as well as the changes in dimensionless velocity. We find that as the Reynolds number increases, the phase interface curls up at multiple locations due to Kelvin-Helmholtz instability, making the fluid more prone to dispersion and fragmentation. This study also simulates the evolutionary processes of RTI under different interface perturbations. These results demonstrate that RTI first develops at the perturbed interface, with its subsequent evolution inducing instability at a secondary interface.
Effects of molecular collisions on accommodation coefficients under multi-parameter incident conditions
HU Yuhui, CHEN Qi, ZHANG Wei, JIANG Dingwu, LI Jin, QIAO Chenliang
2026, 75 (1): 011002. doi: 10.7498/aps.75.20251261
Abstract +
In rarefied gas flows, accommodation coeffcients (ACs) serve as core parameters for gas-surface interactions and play a crucial role in the accuracy of mesoscopic model simulations. However, there exist significant discrepancies in the ACs obtained by different molecular dynamics simulation methods. To accurately characterize the momentum and energy accommodation properties of rarefied gases with solid surfaces under non-equilibrium conditions, this study systematically investigates the gas-surface interactions between argon molecules and platinum surfaces using molecular dynamics (MD) methods. By using single scattering (SS) and continuous scattering (CS) methods, the effects of gas-gas collisions on tangential momentum accommodation coeffcient (TMAC), normal momentum accommodation coeffcient (NMAC), and energy accommodation coeffcients (EAC) are compared and analyzed, as well as the operating rules of parameters such as surface morphology, surface temperature, incident velocity, and mean free path (MFP). The results demonstrate that gas density exerts a dual effect on momentum and energy accommodation: at smaller MFP, the high gas density within the interaction region impedes the accommodation of subsequent incident molecules with the surface, resulting in lower ACs; at moderate MFP, gas-gas collisions promote the accommodation by increasing the frequency of gas-surface collisions, thereby enhancing ACs. Within the MFP range of 2.0–60.0 nm, the deviation in ACs between the CS and SS methods ranges from –14.88% to 5.21%, validating the dual role of gas density. Furthermore, at larger MFP, the TMAC and NMAC obtained via the CS method exhibit different trends with the increase of MFP across surfaces of varying morphologies. In contrast to gas density, increases in both surface temperature and incident velocity shorten the interaction time, resulting in reduced ACs. Notably, the effect of temperature varies across surfaces with different morphologies: elevated temperatures on smooth surfaces enhance the thermal fluctuations of surface atoms, thereby increasing NMAC, while elevated temperatures on rough surfaces make the rough structures smoother, thereby suppressing accommodation. Under high-speed incident conditions, gas-gas collisions enhance NMAC on smooth surfaces, inhibit both TMAC and NMAC on rough surfaces, and suppress EAC across all surfaces. In addition, the ACs obtained via both the CS and SS methods decrease with the increase of incident velocity on surfaces of different morphologies.
PHYSICS OF GASES, PLASMAS, AND ELECTRIC DISCHARGES

EDITOR'S SUGGESTION

Energetic-particle-driven MHD instability in Heliotron J adjusted via key plasma parameter
ZHONG Yao, NAGASAKI Kazunobu, CHEN Jiahong, CHEN Jian, WANG Zhibin
2026, 75 (1): 010501. doi: 10.7498/aps.75.20251022
Abstract +
A large number of energetic particles (EPs) are generated in the heating process to obtain the high temperature plasma for fusion research. These EPs can resonantly excite various magnetohydrodynamic (MHD) instabilities, including the Alfvén eigenmodes (AEs) and the energetic particle modes (EPMs). The excitation of such MHD instabilities can lead to significant EP losses, which not only degrades the plasma confinement and heating efficiency, but also results in excessive heat loads and damage to plasma-facing components. In this work, the influences of key plasma parameters on the excitation and damping effect of EP-driven MHD instabilities in Heliotron J device are investigated for better understanding of the excitation and transport mechanism of EPs driven MHD in specific device, which is meaningful for achieving stable plasma operation in future fusion devices with different heating methods. In this work, the typical EPs driven MHD instabilities are observed using various diagnostic methods, such as magnetic probes, beam emission spectroscopy (BES), electron cyclotron resonance (ECE) radiometers, and interferometers. Combined with the simulation results from STELLGAP and FAR3D programs, the modulus, radial distribution, and spectral characteristics of different instabilities are analyzed in depth, revealing the evolutions of AEs and EPMs in the Heliotron J device under typical heating conditions. This study quantitatively reveals the driving and suppressing mechanisms of EP-driven instabilities by the electron density (ne), the electron temperature (Te), and the energetic/thermal particle specific pressure (βf/βth) in Heliotron J device, under the conditions of different electron cyclotron resonance heating (ECH) and neutral beam injection (NBI). The results show that different characteristics are obtained under the different magnetic field geometry conditions. The results show that an increase in electron density can reduce the instability intensity by about 40%–60%, and an increase in the specific pressure of energetic particles can double the modal growth rate, while an increase in the specific pressure of hot particles has an inhibitory effect of 20%–50% on the growth rate of the low order modes. These findings are useful for understanding the different effects of ECH and NBI on the EPs driven MHD instabilities, and they are also helpful for achieving stable operation by adjusting the heating system parameters in the stellarator-like devices in the future.
Multiple diagnostic techniques measured neutral gas temperatures in N2 plasma and Ar-N2 mixed plasma
AN Yanlin, ZHAO Mingliang, LUO Qian, GAO Fei, WANG Younian
2026, 75 (1): 010502. doi: 10.7498/aps.75.20251240
Abstract +
Low-temperature inductively coupled radio-frequency plasma is a key plasma source in semiconductor fabrication, where the neutral gas temperature (Tg) is one of the critical parameters influencing chemical reactions and plasma characteristics. Precise control of Tg significantly influences processes such as thin-film deposition and reactive ion etching, with its synergistic interaction with plasma parameters (ne, Te) often determining process outcomes. Consequently, a thorough understanding of the evolution of Tg and its correlation with discharge parameters has become a critical issue for optimizing semiconductor manufacturing processes. To achieve more accurate measurements of neutral gas temperature, this work employs three temperature measurement techniques: spectroscopy, Bragg grating, and fiber optic sensing. These methods are used to systematically investigate the variation patterns of neutral gas temperature (Tg) in nitrogen plasma and nitrogen-argon mixed plasma under different radio-frequency power, gas pressure, and gas composition conditions. To elucidate the gas heating mechanism, this work combines Langmuir probe measurements of electron density, electron temperature, electron energy probability distribution with a global model simulation. The results show that as the RF power increases, the energy coupled to the plasma increases, the ionization reaction is enhanced, and the collision process and energy transfer between electrons and neutral particles increase, resulting in a monotonically increasing trend of Tg. When gas pressure initially increases, both electron density and background gas density rise together, enhancing heating efficiency and driving rapid Tg growth. However, beyond 3 Pa, electron mean free path shortens and electron density declines. In contrast, background gas density continues to increase, leading to slower Tg growth. In nitrogen/argon mixed system discharges, increasing the argon proportion significantly enhances the rate of Tg increase. This occurs because a higher argon ratio elevates the proportion of high-energy electrons and electron density, thereby strengthening ionization and neutral gas heating. At the same time, argon metastable atoms enhance the density of excited nitrogen particles through the Penning process, which promotes nitrogen molecular excitation to higher energy levels and further heats the gas. Additionally, we observe that the radial temperature distribution in pure nitrogen plasma shifts from parabolic to saddle-type with axial height increasing, due to intensified electron collision excitation near the coil under electromagnetic field effects. In this study, it is also found that the glass transition temperature at the radial edge remains virtually unchanged as atmospheric pressure increases. This is because, as pressure continues to rise, electrons beneath the coil struggle to migrate to the radial edge to collide with neutral particles, thereby limiting the heating of edge neutral particles.
CONDENSED MATTER: STRUCTURAL, MECHANICAL, AND THERMAL PROPERTIES
Electronic structure and optical property regulation of two-dimensional monolayer FeGa2S4
SONG Rui, CHENG Run, FENG Kai, YAO Jia, WANG Bili, LU Mengjie, AN Ming
2026, 75 (1): 010703. doi: 10.7498/aps.75.20251180
Abstract +
This study aims to explore two-dimensional semiconductor materials with superior carrier transport properties to meet the growing demands of high-speed electronics and optoelectronic devices, focusing on evaluating the feasibility of monolayer FeGa2S4 as a candidate material through systematic theoretical investigations. First-principles calculations are used to analyze the exfoliation energy of FeGa2S4 bulk crystal, as well as the structural stability, mechanical properties, and strain-dependent optoelectronic behavior of its monolayer counterpart. Strain engineering strategies, including uniaxial and biaxial strain, are used to assess carrier mobility modulation and spectral response. Our calculation results indicate that monolayer FeGa2S4 is an indirect bandgap semiconductor (Eg = 1.65 eV) with low stiffness (Young’s modulus up to 151.6 GPa) and high flexibility (Poisson’s ratio less than 0.25), demonstrating exceptional thermodynamic stability. Under +5% uniaxial tensile strain, its electron mobilities along x and y directions dramatically increases to 5402.4 cm2·V–1·s–1 and 4164.0 cm2·V–1·s–1, fivefold higher than its hole mobility. Biaxial strain outperforms uniaxial strain in bandgap modulation and induces a systematic redshift in optical spectra, significantly enhancing visible-light harvesting efficiency. This work reveals that monolayer FeGa2S4 is a promising high-mobility photoactive material for next-generation solar cells and optoelectronics. The strain-mediated control of electronic and optical properties provides a theoretical framework for optimizing 2D semiconductors and critical guidance for experimental synthesis and device engineering. These findings highlight the potential of materials in advancing energy conversion technology and photonic applications.
Conductive behavior and mechanism of carbon rods during preparing porous aluminum oxide by anodization
YANG Shumin, LI Xin, GU Jianjun, QI Yunkai
2026, 75 (1): 010802. doi: 10.7498/aps.75.20251029
Abstract +
Porous anodic aluminum oxide (AAO) films, due to their excellent dielectric, mechanical, and optical properties, have been widely used in electronic devices, catalytic supports, and optical materials. Anodization is the primary method for fabricating high-quality porous AAO films. The conductive behavior and mechanism of commonly used carbon rod counter electrodes are significant factors influencing the microstructure and properties of the films. In this study, a phosphoric acid solution with a mass fraction of 6% is used as the electrolyte, circular aluminum foil serves as the anode, and carbon rods are used as the counter electrodes spaced 15 cm apart. The oxidation time is fixed at 40 s. The conductive behaviors of the carbon rod under oxidation voltages ranging from 100 to 140 V are experimentally investigated. The results show that the pore depth and diameter of the AAO film symmetrically decrease from the film center toward the edges. When the oxidation voltage is below 110 V, the gradients of pore depth and diameter from the center outward are relatively small, resulting in a macroscopically uniform structural color. At an oxidation voltage of 110 V, the gradients of pore depth and diameter increase significantly, resulting in iridescent concentric ring structural colors. As the voltage increases further, the gradients become more pronounced, the number of structural color rings increases, and the visible color gamut significantly broadens. Electromagnetic and electrochemical theories are utilized to calculate the conductive behaviors of the carbon rod under different oxidation voltages and to analyze its conduction mechanism. The carbon rod is found to exhibit “quasi-point electrode” conductive characteristics, with the selection of point electrode positions on the carbon rod following the principle of minimizing the resistance between the two electrodes. This finding not only enriches the electrochemical theory of anodization but also provides theoretical and experimental support for fabricating multifunctional AAO films.
Structural evolution and phase transition behavior of Na0.5Bi0.5TiO3 under high pressure
WANG Runji, FANG Leiming, HE Ruiqi, LENG Haojie, LIU Yongbo, CHEN Xiping, XIE Lei, FENG Qiu, SUN Anwei, XIONG Zhengwei, GAO Zhipeng
2026, 75 (1): 010807. doi: 10.7498/aps.75.20251220
Abstract +
Relaxor ferroelectric sodium bismuth titanate (Na0.5Bi0.5TiO3, NBT) exhibits outstanding ferroelectric characteristics and is widely recognized as a highly promising lead-free ferroelectric material. In order to further promote the application of this environmentally friendly ferroelectric material, it is crucial to gain a comprehensive understanding of its structural evolution and phase transition mechanism under high pressure. This study investigates the structural evolution of NBT under hydrostatic pressure up to 6.8 GPa by integrating in situ high-pressure neutron diffraction experiments with first-principles calculations. Based on high-pressure neutron diffraction experiments conducted at the China Mianyang Research Reactor (CMRR), Rietveld refinement analysis identifies a phase transition from the ambient-pressure R3c phase to the high-pressure Pnma phase in NBT, with a coexistence pressure range of 1.1–4.6 GPa. The bulk modulus of the high-pressure phase Pnma is experimentally determined to be 108.6 GPa for the first time. First-principles calculations further support the thermodynamic tendency for the pressure-induced phase transition from R3c to Pnma and produce a bulk modulus that is in close agreement with the experimental value. By correlating with the experimentally obtained trends of the internal [TiO6] oxygen octahedral structural changes under high pressure in both phases, this study demonstrates that the difference in their macroscopic compressibility originates from the significantly higher pressure sensitivity of the oxygen octahedral distortion degree in the R3c phase than that of the Pnma phase. This relatively softer internal microstructure results in a lower bulk modulus than that of the Pnma phase. By providing a detailed analysis of the pressure-induced phase transition and microstructural evolution, this study clarifies the relationship between the microscopic structural features of the high-pressure and ambient-pressure phases of NBT and their influence on macroscopic mechanical properties, thereby establishing a fundamental connection between microscopic structural responses and bulk physical behavior under high-pressure conditions. These findings provide crucial experimental data and theoretical support for further improving the high-pressure performance and applications of lead-free ferroelectric materials.
Erratum: Reconstruction of gappy data for experiments of flow past a circular cylinder based on deep learning method
ZHANG Fan, ZHANG Heng, LI Zhuoyue, WEN Jun, HU Haibao
2026, 75 (1): 019901. doi: 10.7498/aps.75.019901
Abstract +

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