Highlights
SPECIAL TOPIC—2D materials and future information devices·COVER ARTICLE
COVER ARTICLE
2025, 74 (17): 178501.
doi: 10.7498/aps.74.20250648
Abstract +
Two-dimensional (2D) semiconductor materials exhibit tremendous potential for post-Moore integrated circuits due to their unique physical properties and superior electrical characteristics. However, critical challenges in polarity modulation and complementary integration have significantly hindered the practical applications of 2D materials. The development of compatible polarity-modulation techniques has emerged as a critical step in achieving device functional integration for constructing 2D materials-based complementary circuits. This study innovatively proposes a one-step-annealing-driven polarity-modulation strategy for 2D semiconductors. It is demonstrated in this study that the conduction behavior of Pd-contacted WSe2 transistors transitions from n-type to p-type dominance after annealing, while Cr-contacted devices maintain n-type dominance. Based on this polarity-modulation strategy, by selectively fabricating source and drain electrodes with different metal materials (Pd and Cr) on the same WSe2, combined with a one-step annealing process, the monolithic integration of complementary transistors is achieved, thereby realizing inverter function through device interconnection. The fabricated inverters exhibit a high voltage gain of 23 and a total noise margin of 2.3 V(0.92 Vdd) at an applied Vdd of 2.5 V. This work not only establishes a novel technical pathway for polarity modulation in 2D materials but also provides crucial technological support for developing 2D semiconductor-based complementary logic circuits.
SPECIAL TOPIC—High-pressure modulation and in situ characterization of optoelectronic properties
EDITOR'S SUGGESTION
2025, 74 (17): 170701.
doi: 10.7498/aps.74.20250635
Abstract +
Piezochromic luminescent materials with multi-color switching have received considerable attention in fields such as displays, sensors, and biomedicine. However, enhancing the sensitivity of piezochromic color change through rational molecular design remains a significant challenge. Herein, we report the design, synthesis and high-pressure study of two 9-fluorenone derivatives of DPA (diphenylamine)-FO and DMAcr (9,9-dimethylcarbazine)-FO, realizing pronounced piezochromic phenomena in both emission colors and crystal colors. DPA-FO features a classic donor–acceptor molecular architecture. Its emission wavelength is highly sensitive to the solvent polarity, and as polarity increases, the redshift continues, indicating the emission nature of intramolecular charge transfer (ICT) luminescence. Under pressure, the emission color gradually changes from yellow to reddish brown, and a pressure coefficient of the emission wavelength is 10.7 nm/GPa. To amplify the piezochromic response, the donor unit is strategically modified by replacing the DPA group with DMAcr, a donor with stronger electron-donating ability. The resulting compound, DMAcr-FO, exhibits a more pronounced ICT process, as evidenced by its higher sensitivity of luminescence to solvent polarity. Under pressure, its emission color gradually changes from yellow to deep red. Correspondingly, the pressure coefficient of the emission wavelength increases 17.5 nm/GPa. Pressure-dependent UV-Vis absorption spectra reveal a continuous redshift in the absorption edge of both derivatives, attributed to structural shrinkage caused by enhanced orbital coupling. Notably, DMAcr-FO exhibits more significant changes in absorption edge and Stokes shift, indicating more substantial structural deformation under pressure. In addition, compared with DPA-FO, the infrared (IR) modes of DMAcr-FO present higher shifting rates with the increase of pressure, which also supports the above conclusion. Meanwhile, with the increase of pressure, the considerable structural distortion is also one of the factors that make DMAcr-FO has a more significant piezochromic phenomenon. This study not only deepens the understanding of structure–property relationships in piezochromic materials but also offers a viable strategy for designing high-performance piezo-responsive luminophores through tailored molecular engineering.
SPECIAL TOPIC—Research progress on nickelate superconductors
EDITOR'S SUGGESTION
2025, 74 (17): 177103.
doi: 10.7498/aps.74.20250604
Abstract +
The bilayer nickelate La3Ni2O7, a member of the Ruddlesden–Popper series, has recently received significant attention due to its superconductivity under high pressure (above 14 GPa) with a transition temperature of approximately 80 K. Its unique bilayer structure results in an electronic configuration significantly different from those observed in cuprates and infinite-layer nickelates. Consequently, understanding its correlated electronic structure and superconducting mechanism has become a topic of major scientific importance. Recent experimental observations have further identified the coexistence of charge and spin density wave orders in La3Ni2O7, suggesting a complex interplay between various competing electronic phases and superconductivity.In this work, the charge order in La3Ni2O7 is investigated using a low-energy effective model that explicitly includes the Ni-eg orbitals. By employing a combined density functional theory and dynamical mean-field theory (DFT+DMFT) framework, the influences of the nearest-neighbor Coulomb interaction V on charge ordering and electronic correlation effects are investigated, with nonlocal interactions treated at the Hartree approximation level. Our computational method features a newly developed tensor-network impurity solver, in which a natural-orbital basis and complex-time evolution are utilized, facilitating efficient and accurate evaluation of the Green's function on the real-frequency axis. Our analysis indicates that for interaction strengths below a critical value ($ V \leqslant V_{{\mathrm{c}}1} \approx 0.46 $ eV), the system retains sublattice symmetry, resulting in minimal changes of the spectral function. Several high-energy fine structures identified within the Hubbard bands correspond to the residual atomic multiplet excitations, enabling the extraction of effective Hubbard parameters. When $ V>V_{{\mathrm{c}}1} $, the sublattice symmetry is disrupted and the system transitions to a charge-ordered state. Spectral features systematically evolve with the increase of charge order, providing a clear benchmark for quantitatively evaluating the degree of charge disproportionation based on experimental data. The quasiparticle weight Z exhibits a nonmonotonic behavior with the increase of V, reaching a minimum value of nearly $ V \approx 0.60 $ eV in the more populated sublattice as it approaches half-filling. When the interaction further increases beyond $ V_{{\mathrm{c}}2} \approx 0.63 $ eV, the system becomes fully charged polarized, characterized by one sublattice becoming almost empty and the other substance being nearly three-quarters filled.These findings underscore the critical role of nonlocal Coulomb interactions in driving charge disproportionation and regulating electron correlation, thereby providing new insights into the low-energy ordering phenomena of bilayer nickelates.
SPECIAL TOPIC—High-pressure modulation and in situ characterization of optoelectronic properties
EDITOR'S SUGGESTION
2025, 74 (17): 177801.
doi: 10.7498/aps.74.20250893
Abstract +
HfS2, as a typical IVB group transition metal dichalcogenide (TMD) material, has shown great potential applications in various fields such as photo-sensing, communication, and imaging due to its high carrier mobility and interlayer current density characteristics. Recent studies have revealed the significant role of pressure in modulating the spectral response range and electrical transport properties of TMDs, which has aroused our interest in studying the pressure regulation of the optoelectronic properties of HfS2. In this study, diamond anvil cell based high-pressure in-situ photocurrent, Raman scattering spectroscopy, alternating current impedance spectroscopy, ultraviolet-visible absorption spectroscopy measurements, and combined first-principles calculations are used to systematically investigate the effects of pressure on the electrical transport and optoelectronic properties of HfS2. The experimental results show that the photocurrent of HfS2 continuously increases with pressure rising. Within a pressure range of 0–10.2 GPa, the photocurrent and response of HfS2 show a rapid upward trend with pressure rising; at 10.2 GPa, the photocurrent and response of HfS2 (Iph = 0.32 μA, R = 8.19 μA/W) are about three orders of magnitude higher than their initial values at 0.5 GPa (Iph = 1.40 × 10–4 μA, R = 3.56 × 10–3 μA/W). At the pressure above 10.2 GPa, the growth rate of photocurrent and response slow down significantly, which are related to the structural phase transition of HfS2 near 10.0 GPa. Further compression to 30.1 GPa results in a maximum photocurrent of 3.35 μA, which is five orders of magnitude higher than its initial value at 0.5 GPa. This significant enhancement is attributed to the strengthening of S-S interlayer interaction forces under pressure, which leads band gap and resistivity to decrease. In addition, based on the modified Becke-Johnson (mBJ) exchange-correlation potential, the electronic band structure and optical properties of HfS2 in its initial phase are calculated and analyzed using WIEN2K software package. The calculation results show that with the increase of pressure, the optical absorption coefficient and the real part of the photoconductivity of HfS2 along the c-axis significantly increase, which further reveals the intrinsic physical mechanism of the enhanced photoresponse of HfS2 under pressure. This study offers a new insight into pressure regulated optoelectronic properties of layered materials.
SPECIAL TOPIC—High-pressure modulation and in situ characterization of optoelectronic properties
EDITOR'S SUGGESTION
2025, 74 (17): 178503.
doi: 10.7498/aps.74.20250693
Abstract +
As a core component of modern optoelectronic systems, photodetectors play an indispensable role in optical communications, environmental monitoring, medical imaging, and military detection. With the rapid development of related technologies, the development of novel photodetector materials featuring high sensitivity, fast response, and excellent stability has become a key research focus. Among various candidate materials, A2BX6-type vacancy-ordered double perovskites have attracted significant attention due to their unique crystal structures and outstanding optoelectronic properties. These materials not only possess tunable bandgap structures and high carrier mobility but also demonstrate excellent environmental stability, showing broad application prospects in the field of photodetection. In this study, the optoelectronic response behaviors of a representative lead-free double perovskite, Cs2TeCl6, under high-pressure conditions are systematically investigated. Precise experimental observations reveal an anomalous transition in photocurrent from decrease to increase when the pressure reaches 21.7 GPa. By employing advanced characterization techniques, including high-pressure in situ Raman spectroscopy, UV-Vis absorption spectroscopy, and synchrotron X-ray diffraction, the underlying physical mechanism are elucidated: At the critical pressure of 18 GPa, the material enters an intensified compression stage, leading to a significantly accelerated bandgap narrowing rate. This continuous reduction in bandgap effectively mitigates the weak absorption limitation of the indirect bandgap, enabling efficient absorption of previously unexcitable low-energy photons and ultimately resulting in enhanced photocurrent. This finding not only clarifies the intrinsic relationship between the structure and optoelectronic properties of Cs2TeCl6 at a microscopic level, but, more importantly, offers new insights into regulating the optoelectronic performance of perovskite materials through pressure engineering. These outcomes in this work provide important guidance for developing novel high-performance photodetection devices and establish a valuable research method of optimizing other semiconductor materials. In the future, by further refining material compositions and pressure modulation strategies, the design and fabrication of more efficient and stable photodetector materials can be anticipated.
SPECIAL TOPIC—Research progress on nickelate superconductors
EDITOR'S SUGGESTION
2025, 74 (17): 177401.
doi: 10.7498/aps.74.20250696
Abstract +
Recent experimental studies on the bilayer Ruddlesden-Popper phase nickelate La3Ni2O7 have shown that in the superconducting region, its superconducting transition temperature decreases monotonically from 83 K at 18 GPa as pressure further increases, exhibiting a nearly right-triangular temperature-pressure phase diagram that is different from the dome-shaped diagrams observed in cuprates and iron-based superconductors under either doping or pressure. It is important to understand this anomalous phase diagram in elucidating the superconducting mechanism of La3Ni2O7. Since the electron-phonon coupling mechanism cannot account for the high superconducting transition temperatures in nickelate superconductors, in this work, the pressure dependence of the transition temperature is investigated from the perspective of the itinerant electrons picture and the local spin picture. By combining the density functional theory (DFT) and the unbiased singular-mode functional renormalization group (SM-FRG) method, it is found that the pairing symmetry is consistently an $s_\pm$-wave, driven by spin fluctuations that become progressively weakened under pressure, thereby decreasing in the superconducting transition temperature, which is in qualitative agreement with the experimental observation. On the other hand, we estimate that the pressure dependence in the local spin picture contradicts with the experimental result. Therefore, the pressure dependence of superconducting transition temperature is more consistent with the itinerant electrons picture. Admittedly, we only made a rough estimation based on the local spin picture. It is expected that further and more detailed research will be conducted on the pressure dependence of superconducting transition temperature from the local spin picture, providing deeper insights into the underlying superconducting mechanism of La3Ni2O7.
SPECIAL TOPIC—Research progress on nickelate superconductors
EDITOR'S SUGGESTION
2025, 74 (17): 177402.
doi: 10.7498/aps.74.20250856
Abstract +
Nickel-based superconductors have attracted widespread attention due to their electronic configuration similar to that of copper-based high-temperature superconductors. Recently, the discovery of superconductivity with a transition temperature as high as 80 K in the bilayer nickelate La3Ni2O7 under pressure has not only reignited research interest in nickel-based superconductors but also opened new avenues for the study of unconventional superconductivity. Layered nickel-based superconductors are similar to copper- and iron-based superconductors in crystal structure, superconducting properties, and electronic structure, but they also show significant differences. A deeper investigation into the electronic structure of nickel-based superconductors is expected to reveal the mechanisms behind these similarities and differences, which will further offer critical insights into developing a unified theoretical model and deepen the understanding of unconventional superconductivity. Moreover, the study of nonequilibrium ultrafast dynamics offers new perspectives and regulations for unconventional superconductivity, which has become a vital tool. This paper focuses on the electronic structure and ultrafast dynamics of Ruddlesden-Popper phase layered nickel-based superconductors, systematically reviewing the successful applications of angle-resolved photoemission spectroscopy (ARPES) and ultrafast optical spectroscopy in nickel-based superconductivity research. Specifically, the new properties of different nickelates are compared, including strong electron correlation, Hund coupling, non-Fermi liquid behavior, energy gap formation, and ultrafast electron dynamics. These advances offer important experimental insights into elucidating the mechanisms of unconventional superconductivity and characterizing the properties of their normal states in these materials.
SPECIAL TOPIC—Research progress on nickelate superconductors
EDITOR'S SUGGESTION
2025, 74 (17): 177403.
doi: 10.7498/aps.74.20250711
Abstract +
The high-temperature superconductivity in bilayer nickelate La3Ni2O7 under high pressures, which was discovered in 2023, has spurred intensive theoretical and numerical investigations. These studies aim to unravel physical properties of La3Ni2O7 from various aspects, with particular emphasis on its pairing symmetry and underlying superconducting mechanism. Moreover, significant effort has also been made to explore and predict novel nickel-based superconductors related to La3Ni2O7. This article reviews these recent advancements aimed at elucidating the physical properties and superconducting mechanism of La3Ni2O7, whose multi-orbital characteristics and intricate electronic correlations have spawned diverse theories for its pairing mechanism. In this article, the recent findings on La3Ni2O7 are summarized regarding its macroscopic models, pairing symmetry, normal state characteristics, and the structure of spin and charge density waves. Particular attention is paid to the debate surrounding the role of σ-bonding band metallization in superconductivity. Finally, this article also presents an outlook on future studies crucial for advancing our understanding of La3Ni2O7 superconductivity.
SPECIAL TOPIC—2D materials and future information devices
EDITOR'S SUGGESTION
2025, 74 (17): 178502.
doi: 10.7498/aps.74.20250703
Abstract +
Artificial visual system (AVS) has received increasing attention for their transformative potential in fields such as medical diagnostics, intelligent robotics, and machine vision. Traditional silicon-based imaging technologies, however, face significant limitations, including high energy consumption, limited dynamic range, and integration challenges. Two-dimensional (2D) semiconductor materials, such as MoS2, WSe2, and black phosphorus have emerged as promising alternatives due to their atomically thin structure, tunable bandgaps, high carrier mobility, and superior optoelectronic properties. In this work, recent breakthroughs in the integration of 2D materials with AVS are investigated. Highlighted is the development of a reconfigurable four-terminal phototransistor array based on WSe2 and IGZO heterostructures, which enables monocular 3D disparity reconstruction without the need for multiple cameras or active light sources. The system demonstrates a dynamic imaging rate exceeding 33 frames per second and supports real-time sensing, memory storage, and ambipolar mode switching with ultralow power consumption (as low as 142 pW). Key innovations include multifunctional device architectures that simulate the retinal photoreceptors, bipolar cells, and even neural synapses, achieving functions such as image sensing, real-time adaptation, color recognition, motion tracking, and multimodal perception. Furthermore, by simulating the human neurovisual pathways, these 2D material-based devices can potentially realize in-sensor computing and neuromorphic processing, which substantially reduce data transfer bottlenecks and energy overhead. Nonetheless, the field is still in its formative stage. Here, several critical bottlenecks are emphasized: the lack of scalable, defect-controlled synthesis of 2D heterostructures; the limited spectral bandwidth and color fidelity of current photonic components; the immature state of neuromorphic elements, which often lacks stability, long-term memory, and bio-realistic plasticity. Moreover, the practical integration with real-world applications requires compatibility with high-density manufacturing and dynamic, multi-modal environments. In the future, artificial vision platforms, empowered by engineered 2D materials and heterostructures, will develop into highly compact, intelligent, and context-aware agents capable of autonomous perception and interaction in complex real-world settings.
SPECIAL TOPIC—High-pressure modulation and in situ characterization of optoelectronic properties
EDITOR'S SUGGESTION
2025, 74 (17): 176802.
doi: 10.7498/aps.74.20250498
Abstract +
Semiconducting transition metal chalcogenides exhibit layer-dependent bandgaps, strong excitonic effects, and spin-valley coupling, positioning them as promising candidates for optoelectronic applications. In heterostructures formed by van der Waals stacking, interlayer excitons and moiré superlattices have emerged as a unique platform for exploring quantum many-body physics and correlated electronic phases. Subjecting semiconducting transition metal dichalcogenides and their heterostructures to high pressure enables precise, continuous tuning of optoelectronic properties through anisotropic lattice compression, particularly the dramatic reduction of interlayer distances, which greatly enhances interlayer orbital hybridization over traditional tuning methods. This review systematically presents diamond anvil cell techniques for in situ high-pressure characterization and analyzes the pressure-induced evolution in semiconducting transition metal dichalcogenides and their heterostructures. It focuses on four key aspects: 1) Atomic-scale structural phase transitions (e.g., layer sliding) and corresponding electronic band structure modifications, including direct-to-indirect bandgap transitions in monolayers (K-Λ crossover) and metallization/superconductivity; 2) Quantifiable enhancement of interlayer interactions revealed by layer-dependent phonon shifts and spin-orbit splitting amplification, along with the mechanisms of their influence on properties; 3) Modulation of exciton binding states and related mechanisms, covering intralayer excitons, trions and interlayer excitons; 4) Moiré potential modulation where high pressure significantly deepens potentials via interlayer compression. This review particularly highlights the unique capability of high pressure in enhancing interlayer orbital hybridization, thereby inducing exotic quantum phases. Finally, the future research directions in this field are outlined to advance quantum information device design, strongly correlated electron system simulation, and the novel excitonic state exploration.
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