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Quasi-two-dimensional van der Waals ferromagnetic semiconductor CrSiTe3 with wide potential applications in optoelectronics and nanospintronics has aroused the immense interest of researchers due to the coexistence of intrinsic magnetism and semiconductivity. By combining untrafast femtosecond laser and terahertz spectroscopy, including terahertz time-domain spectroscopy, optical pump-terahertz probe spectroscopy and terahertz emission spectroscopy, we carry out systematic investigation into the van der Waals ferromagnetic semiconductor CrSiTe3 crystal. The experimental results indicate that the conductivity of the sample is robust against the temperature change and isotropic terahertz transmission in the ab-plane. Moreover, it is also observed that the photocarriers induced by 800 nm optical pump exhibit a relaxation in the biexponential form and the complex photoconductivity can be well reproduced by the Drude-Smith model. The main relaxation channel of photocarriers is the recombination of electron-hole pairs. With femtosecond pulse illuminating the surface of sample, a strong terahertz radiation signal with a broad band of 0–2 THz is observed. The present study provides the responses of CrSiTe3 to optical and terahertz frequency and offers crucial information for the future design of CrSiTe3-based electronic and optoelectronic devices.
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Keywords:
- van der Waals ferromagnetic semiconductor /
- terahertz spectrum /
- time-resolved spectroscopy
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图 1 CST原子结构的 (a) 俯视图和 (b) 侧视图; (c) 时间分辨的超快光抽运-THz探测实验光路示意图; (d) 基于第一性原理计算的CST的能带图及 (e) 对应的态密度
Figure 1. Schematic illustration of the crystal structure of CST seen from (a) the top view and (b) the side view; (c) experimental setup for time-resolved ultrafast optical pump-THz probe spectroscopy; (d) the calculated band structure and (e) density of states of CST single crystal by means of the first-principle with the Vienna ab Initio Simulation Package.
图 2 (a) 透过CST样品后的THz时域信号 (蓝色) 与没有样品时的参考信号 (红色); (b) 计算的CST在THz波段的折射率
Figure 2. (a) The THz-TDS signal through the sample (blue) and the reference signal (red) without placing sample; (b) the calculated refractive index of CST in THz frequency range.
图 3 (a) CST温度依赖的THz-TDS及 (b) 经过傅里叶变换后的频谱; 室温下CST晶体方位角0° (c) 和 90° (d)下的3D透射光谱
Figure 3. (a) Temperature dependent THz transmission in time domain and (b) in frequency domain via Fourier transformation; 3D plot of THz transmission of CST crystal at the azimuthal angle 0° (c) and 90° (d) at room temperature.
图 4 (a) 温度5 K、不同抽运功率下的瞬态动力学演化ΔT/T0, 插图为抽运-探测零时间延迟时抽运功率依赖的调制深度, 实线是线性拟合的结果; (b) 通过双指数函数拟合得到的不同抽运功率下的弛豫时间常数; (c) 抽运功率482 μJ/cm2、不同温度下的THz透射响应, 插图为抽运-探测零时间延迟时温度依赖的调制深度; (d) 通过双指数函数拟合得到的不同温度下的弛豫时间常数
Figure 4. (a) The transient dynamics evolution ΔT/T0 under various pump fluence at 5 K, inset gives the fluence dependent modulation depth at the delay time of zero, and the solid line is linear fitting; (b) the decay time constants obtained from biexponential function fitting with respect to pump fluence; (c) the THz transmission response at different temperature under pump fluence of 482 μJ/cm2, inset gives the temperature dependent modulation depth at the delay time of zero; (d) the decay time constants obtained from biexponential function fitting at different temperature, the solid lines are guide to the eyes.
图 5 (a) 抽运功率603 μJ/cm2、不同抽运-探测延迟时间下的频率分辨的复面电导率 (蓝色和红色的空心点), 实线为Drude-Smith模型拟合的结果; (b) 抽运-探测延迟时间2 ps、不同抽运功率下的复面电导率
Figure 5. (a) The complex frequency-resolved sheet photoconductivity (blue and red circle spots) with a fixed pump fluence of 603 μJ/cm2 measured at various pump-probe time delays. The solid lines are the Drude-Smith model fitting; (b) the complex frequency-resolved sheet photoconductivity with a fixed pump-probe time delay of Δt = 2 ps measured at various pump fluence.
图 6 (a) 透射式THz发射光谱示意图, 入射面为样品的ab面; (b) 功率依赖的THz辐射的峰峰值, 实线为线性拟合的结果; (c) 典型的THz辐射的3D图像, 紫色的线为THz波在时间上的投影, 表明发射的THz波为线偏振的; (d) 图 (c) 中水平和竖直面上的THz波经傅里叶变换后的频谱
Figure 6. (a) Illustration for THz emission spectroscopy with transmission configuration, and the fs pulse is incident on ab-plane of the sample; (b) the peak-to-peak value of THz radiation with respect to the pump fluence, and the solid line represents linear fitting; (c) a typical 3D plot of THz radiation. The purple line shows the projection of the THz wave on time, which indicates the radiant THz wave is linearly polarized; (d) the Fourier transformation spectrum of THz waves corresponding to the horizontal and vertical directions in figure (c).
表 1 抽运功率603 μJ/cm2、不同抽运-探测延迟时间下, 基于Drude-Smith模型拟合的参数
Table 1. The fitting parameters based on the Drude-Smith model at different pump-probe delay time with a excitation fluence of 603 μJ/cm2.
Delay time/ps ωp/1010 Hz τ/fs c 2 8.62 127 –0.3338 5 7.82 109 –0.2768 20 5.12 76 –0.2294 
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表 2 抽运-探测延迟时间Δt = 2 ps、不同抽运功率下, 基于Drude-Smith模型拟合的参数
Table 2. The fitting parameters based on the Drude-Smith model under different pump fluence at delay time Δt = 2 ps.
Fluence/μJ·cm–2 ωp/1010 Hz τ/fs c 241 7.30 85 –0.3212 362 8.36 91 –0.3076 482 8.50 114 –0.3929
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[1] Novoselov K S, Geim A K, Morozov S V, Jiang D, Zhang Y, Dubonos S V, Grigorieva I V, Firsov A A 2004 Science 306 666
Google Scholar
[2] Bhimanapati G R, Lin Z, Meunier V, Jung Y, Cha J, Das S, Xiao D, Son Y, Strano M S, Cooper V R, Liang L, Louie S G, Ringe E, Zhou W, Kim S S, Naik R R, Sumpter B G, Terrones H, Xia F, Wang Y, Zhu J, Akinwande D, Alem N, Schuller J A, Schaak R E, Terrones M, Robinson J A 2015 ACS Nano 9 11509
Google Scholar
[3] Fiori G, Bonaccorso F, Iannaccone G, Palacios T, Neumaier D, Seabaugh A, Banerjee S K, Colombo L 2014 Nat. Nanotech. 9 768
Google Scholar
[4] Mermin N D, Wagner H 1966 Phys. Rev. Lett. 17 1133
Google Scholar
[5] Liu B, Zou Y, Zhang L, Zhou S, Wang Z, Wang W, Qu Z, Zhang Y 2016 Sci. Rep. 6 33873
Google Scholar
[6] Gong C, Zhang X 2019 Science 363 706
[7] Huang B, Clark G, Navarro-Moratalla E, Klein D R, Cheng R, Seyler K L, Zhong D, Schmidgall E, McGuire M A, Cobden D H, Yao W, Xiao D, Jarillo-Herrero P, Xu X 2017 Nature 546 270
Google Scholar
[8] Li H, Ruan S, Zeng Y J 2019 Adv. Mater. 31 e1900065
Google Scholar
[9] Thiel L, Wang Z, Tschudin M A, Rohner D, Gutiérrez-Lezama I, Ubrig N, Gibertini M, Giannini E, Morpurgo A F, Maletinsky P 2019 Science 364 973
Google Scholar
[10] Deng Y, Yu Y, Song Y, Zhang J, Wang N Z, Sun Z, Yi Y, Wu Y Z, Wu S, Zhu J, Wang J, Chen X H, Zhang Y 2018 Nature 563 94
Google Scholar
[11] Chen W, Sun Z, Wang Z, Gu L, Xu X, Wu S, Gao C 2019 Science 366 983
Google Scholar
[12] Li X, Yang J 2014 J. Mater. Chem. C 2 7071
Google Scholar
[13] Lin M-W, Zhuang H L, Yan J, Ward T Z, Puretzky A A, Rouleau C M, Gai Z, Liang L, Meunier V, Sumpter B G, Ganesh P, Kent P R C, Geohegan D B, Mandrus D G, Xiao K 2016 J. Mater. Chem. C 4 315
Google Scholar
[14] Casto L D, Clune A. J, Yokosuk M O, Musfeldt J L, Williams T J, Zhuang H L, Lin M-W, Xiao K, Hennig R G, Sales B C, Yan J-Q, Mandrus D 2015 APL Mater. 3 041515
Google Scholar
[15] Xie Q, Liu Y, Wu M, Lu H, Wang W, He L, Wu X 2019 Mater. Lett. 246 60
Google Scholar
[16] Milosavljević A, Šolajić A, Pešić J, Liu Y, Petrovic C, Lazarević N, Popović Z V 2018 Phys. Rev. B 98 104306
Google Scholar
[17] Zhang J, Cai X, Xia W, Liang A, Huang J, Wang C, Yang L, Yuan H, Chen Y, Zhang S, Guo Y, Liu Z, Li G 2019 Phys. Rev. Lett. 123 047203
Google Scholar
[18] Han P, Wang X, Zhang Y 2019 Adv. Opt. Mater. 8 1900533
[19] Guo J, Cheng L, Ren Z, Zhang W, Lin X, Jin Z, Cao S, Sheng Z, Ma G 2020 J. Phys. Condens. Matter 32 185401
Google Scholar
[20] Huang Y, Yao Z, He C, Zhu L, Zhang L, Bai J, Xu X 2019 J. Phys. Condens. Matter 31 153001
Google Scholar
[21] Gao Y, Kaushik S, Philip E J, Li Z, Qin Y, Liu Y P, Zhang W L, Su Y L, Chen X, Weng H, Kharzeev D E, Liu M K, Qi J 2020 Nat. Commun. 11 720
Google Scholar
[22] Xing X, Zhao L, Zhang Z, Liu X, Zhang K, Yu Y, Lin X, Chen H Y, Chen J Q, Jin Z, Xu J, Ma Guo 2017 J. Phys. Chem. C 121 20451
Google Scholar
[23] Lui C H, Frenzel A J, Pilon D V, Lee Y-H, Ling X, Akselrod G M, Kong J, Gedik N 2014 Phys. Rev. Lett. 113 166801
Google Scholar
[24] Kresse G, Hafner J 1993 Phys. Rev. B 47 558
Google Scholar
[25] Perdew J P, Burke K, Ernzerhof M 1996 Phys. Rev. Lett. 77 3865
Google Scholar
[26] Guo H C, Liu W M, Tang S H 2007 J. Appl. Phys. 102 033105
Google Scholar
[27] Dorney T D, Baraniuk R G, Mittleman D M 2001 J. Opt. Soc. Am. A 18 1562
Google Scholar
[28] Tielrooij K J, Song J C W, Jensen S A, Centeno A, Pesquera A, Elorza A Z, Bonn M, Levitov L S, Koppens F H L 2013 Nat. Phys. 9 248
Google Scholar
[29] Zhang W, Yang Y, Suo P, Zhao W, Guo J, Lu Q, Lin X, Jin Z, Wang L, Chen G, Xiu F, Liu W, Zhang C, Ma G 2019 Appl. Phys. Lett. 114 221102
Google Scholar
[30] Heyman J N, Coates N, Reinhardt A, Strasser G 2003 Appl. Phys. Lett. 83 5476
Google Scholar
[31] Barnes M E, Berry S A, Gow P, McBryde D, Daniell G J, Beere H E, Ritchie D A, Apostolopoulos V 2013 Opt. Express 21 16263
Google Scholar
[32] Rice A, Jin Y, Ma X F, Zhang X C, Bliss D, Larkin J, Alexander M 1994 Appl. Phys. Lett. 64 1324
Google Scholar
[33] Braun L, Mussler G, Hruban A, Konczykowski M, Schumann T, Wolf M, Munzenberg M, Perfetti L, Kampfrath T 2016 Nat. Commun. 7 13259
Google Scholar
[34] Suo P, Xia W, Zhang W, Zhu X, Fu J, Lin X, Jin Z, Liu W, Guo Y, Ma G 2020 Laser Photonics Rev. 14 2000025
Google Scholar
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