1
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Li Y, Shang X, Zhou YH, Zheng X. The effect of light-irradiated area on the spin dependent photocurrent in zigzag graphene nanoribbon junctions. Phys Chem Chem Phys 2023; 25:24428-24435. [PMID: 37655683 DOI: 10.1039/d3cp01176c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 09/02/2023]
Abstract
In this work, we study the photogalvanic effect of a zigzag graphene nanoribbon junction with a centro-symmetrical structure which consists of 8 zigzag chains by density functional calculations. Specifically, we focus on the cases where the irradiated region is just part of the central region and located at different positions, with an aim to see how the spin dependent photocurrents will change and whether pure spin current can be obtained. It is found that the magnitude of the spin-dependent photocurrents increases with a gradual increase of the irradiated region and pure spin current is achieved when and only when the entire central region is irradiated. In addition, we studied the additive effect in this device to see that if we divide the central region into two parts, whether the sum of the spin current generated by irradiating the two parts individually is equal to that produced when the entire central region is irradiated. It is found that the sum of the spin currents produced by irradiating the two parts individually is smaller than that obtained by irradiating the whole central region, which means that the rule of "1 + 2 = 3" does not hold and the coupling effect between the two parts is important in photocurrent generation.
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Affiliation(s)
- Yuejun Li
- College of Science, East China Jiao Tong University, Nanchang 330013, China.
- College of Information Science and Technology, Nanjing Forestry University, Nanjing 210037, China.
| | - Xiaofei Shang
- College of Science, East China Jiao Tong University, Nanchang 330013, China.
| | - Yan-Hong Zhou
- College of Science, East China Jiao Tong University, Nanchang 330013, China.
| | - Xiaohong Zheng
- College of Information Science and Technology, Nanjing Forestry University, Nanjing 210037, China.
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2
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Liu J, Niu J, Ma Y, Chi F, Yi Z, Liu L. Linear photogalvanic effects in monolayer ternary metallic compound Na 2MgSn. OPTICS EXPRESS 2023; 31:28040-28050. [PMID: 37710867 DOI: 10.1364/oe.494763] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/04/2023] [Accepted: 06/19/2023] [Indexed: 09/16/2023]
Abstract
The linear photogalvanic effect (LPGE) is investigated by using the non-equilibrium Green's function (NEGF) technique combined with density functional theory (DFT) in monolayer Na2MgSn. We consider the cases of three different central regions, which are pure Na2MgSn, Na-vacancy, and Pb-substituted. It is found that both pure and defective Na2MgSn monolayers induce photoresponse under linearly polarized light. The photoresponse varies periodically as a form of either sinusoidal or cosinoidal function of the polarization angle. In the near-infrared and visible ranges, the photoresponse is more sensitive to the long wave range of visible light. In the case of single-atom defects, the photoresponse with Na-vacancy is larger than that of pb-substitution defects. Compared with the other two central regions, the maximum extinction ratio (ER) of Na-vacancy is larger, so it has higher polarization sensitivity. When the location of Na-vacancy is adjusted, the photoresponse changes obviously, and the Na 1*- vacancy has the largest photoresponse. With the increase of the Na-vacancy concentration, the photoresponse changes nonlinearly but is smaller than that of a single vacancy. A small bias voltage can greatly improve the photoresponse. Our results suggest an effective method to enhance the photoresponse and show the promise of Na2MgSn monolayers in optical detection.
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3
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Ashoka A, Nagane S, Strkalj N, Sharma A, Roose B, Sneyd AJ, Sung J, MacManus-Driscoll JL, Stranks SD, Feldmann S, Rao A. Local symmetry breaking drives picosecond spin domain formation in polycrystalline halide perovskite films. NATURE MATERIALS 2023; 22:977-984. [PMID: 37308547 DOI: 10.1038/s41563-023-01550-z] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/04/2022] [Accepted: 04/06/2023] [Indexed: 06/14/2023]
Abstract
Photoinduced spin-charge interconversion in semiconductors with spin-orbit coupling could provide a route to optically addressable spintronics without the use of external magnetic fields. However, in structurally disordered polycrystalline semiconductors, which are being widely explored for device applications, the presence and role of spin-associated charge currents remains unclear. Here, using femtosecond circular-polarization-resolved pump-probe microscopy on polycrystalline halide perovskite thin films, we observe the photoinduced ultrafast formation of spin domains on the micrometre scale formed through lateral spin currents. Micrometre-scale variations in the intensity of optical second-harmonic generation and vertical piezoresponse suggest that the spin-domain formation is driven by the presence of strong local inversion symmetry breaking via structural disorder. We propose that this leads to spatially varying Rashba-like spin textures that drive spin-momentum-locked currents, leading to local spin accumulation. Ultrafast spin-domain formation in polycrystalline halide perovskite films provides an optically addressable platform for nanoscale spin-device physics.
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Affiliation(s)
- Arjun Ashoka
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Satyawan Nagane
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | - Nives Strkalj
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
| | - Ashish Sharma
- Cavendish Laboratory, University of Cambridge, Cambridge, UK
| | - Bart Roose
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | | | - Jooyoung Sung
- Department of Emerging Materials Science, DGIST, Daegu, Republic of Korea
| | | | - Samuel D Stranks
- Department of Chemical Engineering and Biotechnology, University of Cambridge, Cambridge, UK
| | | | - Akshay Rao
- Cavendish Laboratory, University of Cambridge, Cambridge, UK.
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4
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Liang G, Zhai G, Ma J, Wang H, Zhao J, Wu X, Zhang X. Circular Photogalvanic Current in Ni-Doped Cd 3As 2 Films Epitaxied on GaAs(111)B Substrate. NANOMATERIALS (BASEL, SWITZERLAND) 2023; 13:1979. [PMID: 37446495 DOI: 10.3390/nano13131979] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2023] [Revised: 06/26/2023] [Accepted: 06/28/2023] [Indexed: 07/15/2023]
Abstract
Magnetic element doped Cd3As2 Dirac semimetal has attracted great attention for revealing the novel quantum phenomena and infrared opto-electronic applications. In this work, the circular photogalvanic effect (CPGE) was investigated at various temperatures for the Ni-doped Cd3As2 films which were grown on GaAs(111)B substrate by molecular beam epitaxy. The CPGE current generation was found to originate from the structural symmetry breaking induced by the lattice strain and magnetic doping in the Ni-doped Cd3As2 films, similar to that in the undoped ones. However, the CPGE current generated in the Ni-doped Cd3As2 films was approximately two orders of magnitude smaller than that in the undoped one under the same experimental conditions and exhibited a complex temperature variation. While the CPGE current in the undoped film showed a general increase with rising temperature. The greatly reduced CPGE current generation efficiency and its complex variation with temperature in the Ni-doped Cd3As2 films was discussed to result from the efficient capture of photo-generated carriers by the deep-level magnetic impurity bands and enhanced momentum relaxation caused by additional strong impurity scattering when magnetic dopants were introduced.
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Affiliation(s)
- Gaoming Liang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Guihao Zhai
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jialin Ma
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Hailong Wang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Jianhua Zhao
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xiaoguang Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
| | - Xinhui Zhang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China
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5
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Zhang Y, Nie Y, Wang Y, Xue X, Zhu S, Hu B, Liu Y, Shi L, Chen YH. Local Electric-Field-Induced Spin Photocurrent in ReS 2. J Phys Chem Lett 2022; 13:11689-11695. [PMID: 36512319 DOI: 10.1021/acs.jpclett.2c03480] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/17/2023]
Abstract
A spin-related photocurrent excited by circularly polarized light is observed near the electrodes on a few-layer ReS2 sample at room temperature. For both electrodes, the spatial distribution of the spin photocurrent shows a feature of two wings, with one positive and the other negative. In this work, it is suggested that this phenomenon arises from the inverse spin Hall effect due to the local electric field near the electrode. Bias voltage that modulates this field further controls the sign and magnitude of the spin photocurrent. Our research shows that the electric field near the electrodes has a significant impact on the spin transmission operation, and hence it could be taken into account for manufacturing spintronic devices in the future.
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Affiliation(s)
- Yang Zhang
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing100083, China
| | - Yue Nie
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
| | - Yu Wang
- National Laboratory of Solid State Microstructures, School of Physics, Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing210093, China
| | - Xiaolan Xue
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
| | - Shenbo Zhu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing100049, China
| | - Baoxin Hu
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
| | - Yu Liu
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing100083, China
| | - Liwei Shi
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou221116, China
| | - Yong-Hai Chen
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing100083, China
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing100049, China
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6
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Wang S, Zhang H, Zhang J, Li S, Luo D, Wang J, Jin K, Sun J. Circular Photogalvanic Effect in Oxide Two-Dimensional Electron Gases. PHYSICAL REVIEW LETTERS 2022; 128:187401. [PMID: 35594114 DOI: 10.1103/physrevlett.128.187401] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2021] [Revised: 11/24/2021] [Accepted: 03/28/2022] [Indexed: 06/15/2023]
Abstract
Two-dimensional electron gases (2DEGs) at the LaAlO_{3}/SrTiO_{3} interface have attracted wide interest, and some exotic phenomena are observed, including 2D superconductivity, 2D magnetism, and diverse effects associated with Rashba spin-orbit coupling. Despite the intensive investigations, however, there are still hidden aspects that remain unexplored. For the first time, here we report on the circular photogalvanic effect (CPGE) for the oxide 2DEG. Spin polarized electrons are selectively excited by circular polarized light from the in-gap states of SrTiO_{3} to 2DEG and are converted into electric current via the mechanism of spin-momentum locking arising from Rashba spin-orbit coupling. Moreover, the CPGE can be effectively modified by the density and distribution of oxygen vacancies. This Letter presents an effective approach to generate and manipulate the spin polarized current, paving the way toward oxide spintronics.
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Affiliation(s)
- Shuanhu Wang
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Hui Zhang
- School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, China
| | - Jine Zhang
- School of Integrated Circuit Science and Engineering, Beihang University, Beijing 100191, China
| | - Shuqin Li
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Dianbing Luo
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Jianyuan Wang
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Kexin Jin
- Shaanxi Key Laboratory of Condensed Matter Structures and Properties and MOE Key Laboratory of Materials Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710072, China
| | - Jirong Sun
- Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
- Songshan Lake Materials Laboratory, Dongguan, Guangdong 523808, China
- Spintronics Institute, University of Jinan, Jinan, Shandong 250022, China
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7
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Wu W, Yu J, Xia L, Zhu K, Zeng X, Chen Y, Yin C, Cheng S, Lai Y, He K. Giant photoinduced inverse spin Hall effect of the surface states in three dimensional topological insulators Bi 2Te 3 with different thickness. OPTICS EXPRESS 2022; 30:15085-15095. [PMID: 35473239 DOI: 10.1364/oe.456150] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/14/2022] [Accepted: 03/30/2022] [Indexed: 06/14/2023]
Abstract
The photoinduced inverse spin Hall effect (PISHE) has been studied in three dimensional (3D) topological insulator (TI) Bi2Te3 thin films with different thicknesses (3, 5, 12 and 20 quintuple layer (QL)). The sign of the PISHE current flips only once in the 3- and 20-QL Bi2Te3 films, but it flips three times in the 5-, 7- and 12-QL samples. The three-times sign flip is due to the superposition of the PISHE current of the top and bottom surface states in Bi2Te3 films. By analyzing the x-ray photoelectron spectroscopy (XPS) of the Bi2Te3 films, we find that the top surface of the 3- and 20-QL Bi2Te3 films are severely oxidized, leading to only one sign flip in the PISHE. The PISHE contributed by the top and bottom surface states in Bi2Te3 films have been successfully separated by fitting a theoretical model to the PISHE current. The impact of the bulk states on PISHE current has been determined. The PISHE current is also measured at different light powers, and all the measurement results are in good agreement with the theoretical model. In addition, it is found that the PISHE current in Bi2Te3 films grown on Si substrate is more than two orders larger than that grown on SrTiO3 substrates, which can be attributed to the larger absorption coefficient for Bi2Te3/Si samples. It is revealed that the PISHE current in 3D TI Bi2Te3 is as large as 140 nA/W in the 3-QL Bi2Te3 film grown on Si substrate, which is more than one order larger than that reported in GaAs/AlGaAs heterojunction (about 2 nA/W) and GaN/AlGaN heterojunction (about 1.7 nA/W). The giant PISHE current demonstrates that the TIs with strong SOC may have good application prospects in spintronic devices with high spin-to-charge conversion efficiency.
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8
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Liang G, Zhai G, Ma J, Wang H, Zhao J, Wu X, Zhang X. Strain-induced circular photogalvanic current in Dirac semimetal Cd 3As 2 films epitaxied on a GaAs(111)B substrate. NANOSCALE 2022; 14:2383-2392. [PMID: 35088779 DOI: 10.1039/d1nr05812f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/14/2023]
Abstract
Dirac semimetal (DSM) Cd3As2 has drawn great attention for exploring the novel quantum phenomena and high-speed optoelectronic applications. The circular photogalvanic effect (CPGE) current, resulting from the optically-excited spin orientation transport, was theoretically predicted to vanish in an ideal Dirac system due to the symmetric photoexcitation about the Dirac point. Here, we reported the observation of the CPGE photocurrent in epitaxial Cd3As2 thin films grown on a GaAs(111)B substrate. The signature of the CPGE is confirmed by its sign reversal upon switching the helicity of optical radiation, as well as its dependence on the excitation incident angle and power. By comparison of the CPGE response between the films with different thicknesses, it is suggested that the observed CPGE results from the reduced structure symmetry and substantially modified electronic band structure of the Cd3As2 thin film that undergoes large epitaxial strain. Our experimental findings provide a valuable reference for the band engineering and exotic helicity-dependent photocurrent phenomena in DSMs towards their potential opto-spintronic device applications.
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Affiliation(s)
- Gaoming Liang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Guihao Zhai
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Jialin Ma
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Hailong Wang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Jianhua Zhao
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Xiaoguang Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Xinhui Zhang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, P. R. China.
- Center of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, P. R. China
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9
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Zhang Y, Liu Y, Xue XL, Zeng XL, Wu J, Shi LW, Chen YH. Current-Induced Spin Photocurrent in GaAs at Room Temperature. SENSORS 2022; 22:s22010399. [PMID: 35009939 PMCID: PMC8749936 DOI: 10.3390/s22010399] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Revised: 12/31/2021] [Accepted: 01/04/2022] [Indexed: 12/04/2022]
Abstract
Circularly polarized photocurrent, observed in p-doped bulk GaAs, varies nonlinearly with the applied bias voltage at room temperature. It has been explored that this phenomenon arises from the current-induced spin polarization in GaAs. In addition, we found that the current-induced spin polarization direction of p-doped bulk GaAs grown in the (001) direction lies in the sample plane and is perpendicular to the applied electric field, which is the same as that in GaAs quantum well. This research indicates that circularly polarized photocurrent is a new optical approach to investigate the current-induced spin polarization at room temperature.
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Affiliation(s)
- Yang Zhang
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou 221116, China; (Y.Z.); (X.-L.X.); (L.-W.S.)
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China; (Y.L.); (X.-L.Z.); (J.W.)
| | - Yu Liu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China; (Y.L.); (X.-L.Z.); (J.W.)
| | - Xiao-Lan Xue
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou 221116, China; (Y.Z.); (X.-L.X.); (L.-W.S.)
| | - Xiao-Lin Zeng
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China; (Y.L.); (X.-L.Z.); (J.W.)
| | - Jing Wu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China; (Y.L.); (X.-L.Z.); (J.W.)
| | - Li-Wei Shi
- School of Materials Science and Physics, China University of Mining and Technology, Xuzhou 221116, China; (Y.Z.); (X.-L.X.); (L.-W.S.)
| | - Yong-Hai Chen
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing Key Laboratory of Low Dimensional Semiconductor Materials and Devices, Beijing 100083, China; (Y.L.); (X.-L.Z.); (J.W.)
- Correspondence:
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10
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Wu J, Hao HM, Liu Y, Zhang Y, Zeng XL, Zhu SB, Niu ZC, Ni HQ, Chen YH. Anomalous circular photogalvanic effect in p-GaAs. OPTICS EXPRESS 2021; 29:13829-13838. [PMID: 33985111 DOI: 10.1364/oe.423121] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 04/14/2021] [Indexed: 06/12/2023]
Abstract
The anomalous circular photogalvanic effect (ACPGE) is observed in p-GaAs with a thickness of 2 μm at room temperature, in which circularly polarized light is used to inject spin-polarized carriers and the spin diffusion can generate a macroscopic detectable charge current due to the inverse spin Hall effect. The normalized ACPGE signals show first increasing and then decreasing with increasing the doping concentration. The role of the doping impurities is discussed by both extrinsic and intrinsic models, and both can well explain the variation of ACPGE with the doping concentration.
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11
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Zhang Y, Liu Y, Zeng XL, Wu J, Yu JL, Chen YH. Distinguishing the inverse spin Hall effect photocurrent of electrons and holes by comparing to the classical Hall effect. OPTICS EXPRESS 2020; 28:8331-8340. [PMID: 32225460 DOI: 10.1364/oe.387692] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Accepted: 02/26/2020] [Indexed: 06/10/2023]
Abstract
The photo-excited electrons and holes move in the same direction in the diffusion and in the opposite direction in the drift under an electric field. Therefore, the contribution to the inverse spin Hall current of photo-excited electrons and holes in the diffusion regime is different to that in the drift regime under electric field. By comparing the classical Hall effect with the inverse spin Hall effect in both diffusion and drift regime, we develop an optical method to distinguish the contributions of electrons and holes in the inverse spin Hall effect. It is found that the contribution of the inverse spin Hall effect of electrons and holes in an InGaAs/AlGaAs un-doped multiple quantum well is approximately equal at room temperature.
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12
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Ji Z, Liu G, Addison Z, Liu W, Yu P, Gao H, Liu Z, Rappe AM, Kane CL, Mele EJ, Agarwal R. Spatially dispersive circular photogalvanic effect in a Weyl semimetal. NATURE MATERIALS 2019; 18:955-962. [PMID: 31308515 DOI: 10.1038/s41563-019-0421-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/18/2018] [Accepted: 06/04/2019] [Indexed: 06/10/2023]
Abstract
Weyl semimetals (WSMs) are gapless topological states of matter with broken inversion and/or time reversal symmetry. WSMs can support a circulating photocurrent when illuminated by circularly polarized light at normal incidence. Here, we report a spatially dispersive circular photogalvanic effect (s-CPGE) in a WSM that occurs with a spatially varying beam profile. Our analysis shows that the s-CPGE is controlled by a symmetry selection rule combined with asymmetric carrier excitation and relaxation dynamics. By evaluating the s-CPGE for a minimal model of a WSM, a frequency-dependent scaling behaviour of the photocurrent is obtained. Wavelength-dependent measurements from the visible to mid-infrared range show evidence of Berry curvature singularities and band inversion in the s-CPGE response. We present the s-CPGE as a promising spectroscopic probe for topological band properties, with the potential for controlling photoresponse by patterning optical fields on topological materials to store, manipulate and transmit information.
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Affiliation(s)
- Zhurun Ji
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Gerui Liu
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Zachariah Addison
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
| | - Wenjing Liu
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA
| | - Peng Yu
- Centre for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore
| | - Heng Gao
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA
| | - Zheng Liu
- Centre for Programmable Materials, School of Materials Science and Engineering, Nanyang Technological University, Singapore, Singapore
| | - Andrew M Rappe
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA, USA
| | - Charles L Kane
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
| | - Eugene J Mele
- Department of Physics and Astronomy, University of Pennsylvania, Philadelphia, PA, USA
| | - Ritesh Agarwal
- Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA.
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Yu J, Zeng X, Wang Y, Xia L, Cheng S, Chen Y, Liu Y, Lai Y, Zheng Q. Observation of Extrinsic Photo-Induced Inverse Spin Hall Effect in a GaAs/AlGaAs Two-Dimensional Electron Gas. NANOSCALE RESEARCH LETTERS 2018; 13:320. [PMID: 30315428 PMCID: PMC6185879 DOI: 10.1186/s11671-018-2715-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 05/16/2018] [Accepted: 09/10/2018] [Indexed: 06/08/2023]
Abstract
The inverse spin Hall effect induced by circularly polarized light has been observed in a GaAs/AlGaAs two-dimensional electron gas. The spin transverse force has been determined by fitting the photo-induced inverse spin Hall effect (PISHE) current to a theoretical model. The PISHE current is also measured at different light power and different light spot profiles, and all the measurement results are in good agreement with the theoretical calculations. We also measure the PISHE current at different temperatures (i.e., from 77 to 300 K). The temperature dependence of the PISHE current indicates that the extrinsic mechanism plays a dominant role, which is further confirmed by the weak dependence of the PISHE current on the crystal orientation of the sample.
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Affiliation(s)
- Jinling Yu
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
- Jiangsu Collaborative Innovation Center of Photovolatic Science and Engineering, Changzhou University, Changzhou, 213164 Jiangsu China
| | - Xiaolin Zeng
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
| | - Yumeng Wang
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
| | - Lijia Xia
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
| | - Shuying Cheng
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
- Jiangsu Collaborative Innovation Center of Photovolatic Science and Engineering, Changzhou University, Changzhou, 213164 Jiangsu China
| | - Yonghai Chen
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083 China
- College of Materials Science and Opto-Electronic Technology, University of Chinese Academy of Sciences, Beijing, 100049 China
| | - Yu Liu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083 China
| | - Yunfeng Lai
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
| | - Qiao Zheng
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University, Fuzhou, China
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14
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Yu J, Zeng X, Zhang L, Yin C, Chen Y, Liu Y, Cheng S, Lai Y, He K, Xue Q. Inverse spin Hall effect induced by linearly polarized light in the topological insulator Bi 2Se 3. OPTICS EXPRESS 2018; 26:4832-4841. [PMID: 29475328 DOI: 10.1364/oe.26.004832] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/22/2017] [Accepted: 02/06/2018] [Indexed: 06/08/2023]
Abstract
The inverse spin Hall effect (ISHE) induced by the normal incidence of linearly-polarized infrared radiation has been observed in the topological insulator Bi2Se3. A model has been proposed to explain the phenomenon, and the spin transverse force has been determined by the model fitting. The anomalous linear photogalvanic effect (ALPGE) is also observed, and the photoinduced momentum anisotropy is extracted. Furthermore, the ISHE and ALPGE are investigated at different temperatures between 77 and 300 K, and the temperature dependence of the spin transverse force and photoinduced momentum anisotropy are obtained. This study suggests a new way to investigate the inverse spin Hall effect via linearly polarized light even at room temperature.
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Yu J, Zeng X, Zhang L, He K, Cheng S, Lai Y, Huang W, Chen Y, Yin C, Xue Q. Photoinduced Inverse Spin Hall Effect of Surface States in the Topological Insulator Bi 2Se 3. NANO LETTERS 2017; 17:7878-7885. [PMID: 29141404 DOI: 10.1021/acs.nanolett.7b04172] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
The three-dimensional (3D) topological insulator (TI) Bi2Se3 exhibits topologically protected, linearly dispersing Dirac surface states (SSs). To access the intriguing properties of these SSs, it is important to distinguish them from the coexisting two-dimensional electron gas (2DEG) on the surface. Here, we use circularly polarized light to induce the inverse spin Hall effect in a Bi2Se3 thin film at different temperatures (i.e., from 77 to 300 K). It is demonstrated that the photoinduced inverse spin Hall effect (PISHE) of the top SSs and the 2DEG can be separated based on their opposite signs. The temperature and power dependence of the PISHE also confirms our method. Furthermore, it is found that the PISHE in the 2DEG is dominated by the extrinsic mechanism, as revealed by the temperature dependence of the PISHE.
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Affiliation(s)
- Jinling Yu
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University , Fuzhou 350108, Fujian, China
| | - Xiaolin Zeng
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University , Fuzhou 350108, Fujian, China
| | - Liguo Zhang
- Department of Physics, State Key Laboratory of Low Dimensional Quantum Physics, Tsinghua University , Beijing 100084, China
| | - Ke He
- Department of Physics, State Key Laboratory of Low Dimensional Quantum Physics, Tsinghua University , Beijing 100084, China
| | - Shuying Cheng
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University , Fuzhou 350108, Fujian, China
- Jiangsu Collaborative Innovation Center of Photovolatic Science and Engineering, Changzhou University , Changzhou 213164, Jiangsu China
| | - Yunfeng Lai
- Institute of Micro/Nano Devices and Solar Cells, School of Physics and Information Engineering, Fuzhou University , Fuzhou 350108, Fujian, China
- Jiangsu Collaborative Innovation Center of Photovolatic Science and Engineering, Changzhou University , Changzhou 213164, Jiangsu China
| | - Wei Huang
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083, China
| | - Yonghai Chen
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences , Beijing 100083, China
- College of Materials Science and Optoelectronic Technology, University of Chinese Academy of Sciences , Beijing 100049, China
| | - Chunming Yin
- School of Physics, University of New South Wales , Sydney, New South Wales 2052, Australia
- CAS Key Laboratory of Microscale Magnetic Resonance, Department of Modern Physics, Synergetic Innovation Center of Quantum Information and Quantum Physics, University of Science and Technology of China , Hefei 230026, China
| | - Qikun Xue
- Department of Physics, State Key Laboratory of Low Dimensional Quantum Physics, Tsinghua University , Beijing 100084, China
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16
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Ramin Moayed MM, Bielewicz T, Zöllner MS, Herrmann C, Klinke C. Towards colloidal spintronics through Rashba spin-orbit interaction in lead sulphide nanosheets. Nat Commun 2017; 8:15721. [PMID: 28589933 PMCID: PMC5467232 DOI: 10.1038/ncomms15721] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2016] [Accepted: 04/20/2017] [Indexed: 11/18/2022] Open
Abstract
Employing the spin degree of freedom of charge carriers offers the possibility to extend the functionality of conventional electronic devices, while colloidal chemistry can be used to synthesize inexpensive and tunable nanomaterials. Here, in order to benefit from both concepts, we investigate Rashba spin-orbit interaction in colloidal lead sulphide nanosheets by electrical measurements on the circular photo-galvanic effect. Lead sulphide nanosheets possess rock salt crystal structure, which is centrosymmetric. The symmetry can be broken by quantum confinement, asymmetric vertical interfaces and a gate electric field leading to Rashba-type band splitting in momentum space at the M points, which results in an unconventional selection mechanism for the excitation of the carriers. The effect, which is supported by simulations of the band structure using density functional theory, can be tuned by the gate electric field and by the thickness of the sheets. Spin-related electrical transport phenomena in colloidal materials open a promising pathway towards future inexpensive spintronic devices.
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Affiliation(s)
| | - Thomas Bielewicz
- Institute of Physical Chemistry, University of Hamburg, 20146 Hamburg, Germany
| | | | - Carmen Herrmann
- Institute of Inorganic and Applied Chemistry, University of Hamburg, 20146 Hamburg, Germany
| | - Christian Klinke
- Institute of Physical Chemistry, University of Hamburg, 20146 Hamburg, Germany
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17
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Zhu L, Liu Y, Huang W, Qin X, Li Y, Wu Q, Chen Y. Spin transport in undoped InGaAs/AlGaAs multiple quantum well studied via spin photocurrent excited by circularly polarized light. NANOSCALE RESEARCH LETTERS 2016; 11:8. [PMID: 26744148 PMCID: PMC4705080 DOI: 10.1186/s11671-015-1218-3] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 12/27/2015] [Indexed: 06/05/2023]
Abstract
The spin diffusion and drift at different excitation wavelengths and different temperatures have been studied in undoped InGaAs/AlGaAs multiple quantum well (MQW). The spin polarization was created by optical spin orientation using circularly polarized light, and the reciprocal spin Hall effect was employed to measure the spin polarization current. We measured the ratio of the spin diffusion coefficient to the mobility of spin-polarized carriers. From the wavelength dependence of the ratio, we found that the spin diffusion and drift of holes became as important as electrons in this undoped MQW, and the ratio for light holes was much smaller than that for heavy holes at room temperature. From the temperature dependence of the ratio, the correction factors for the common Einstein relationship for spin-polarized electrons and heavy holes were firstly obtained to be 93 and 286, respectively.
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Affiliation(s)
- Laipan Zhu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
- Beijing Institute of Nanoenergy and Nanosystems, Chinese Academy of Sciences, National Center for Nanoscience and Technology (NCNST), Beijing, 100083, People's Republic of China.
| | - Yu Liu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
| | - Wei Huang
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
| | - Xudong Qin
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
| | - Yuan Li
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
| | - Qing Wu
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
| | - Yonghai Chen
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, Beijing, 100083, People's Republic of China.
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18
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Li JB, Wu XG, Wang GW, Xu YQ, Niu ZC, Zhang XH. Helicity-dependent photocurrent induced by the in-plane transverse electric current in an InAs quantum well. Sci Rep 2016; 6:31189. [PMID: 27501858 PMCID: PMC4977544 DOI: 10.1038/srep31189] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2016] [Accepted: 07/13/2016] [Indexed: 11/09/2022] Open
Abstract
We report the observation of a new type of helicity-dependent photocurrent induced by an in-plane transverse direct electric current in an InAs quantum well. The amplitude of the photocurrent depends linearly on the transverse current. Moreover, the observed incident azimuth-angle dependence of this photocurrent is different from that induced by the circular photogalvanic effect. This new photocurrent appears as a result of an asymmetrical carrier distribution in both the conduction and valence bands induced by the transverse current. The photoexcited carrier density created by interband transition processes is thus modulated and leads to the observed new azimuth-angle dependence. The observed efficient generation of the helicity-dependent photocurrent offers an effective approach to manipulate electron spins in two-dimensional semiconductor systems with the added advantage of electrical control of the spin-related photocurrent in spintronic applications.
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Affiliation(s)
- J B Li
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
| | - X G Wu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
| | - G W Wang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
| | - Y Q Xu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
| | - Z C Niu
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
| | - X H Zhang
- State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Science, P. O. Box 912, Beijing 100083, P. R. China
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19
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Spin transport study in a Rashba spin-orbit coupling system. Sci Rep 2014; 4:4030. [PMID: 24504193 PMCID: PMC3916788 DOI: 10.1038/srep04030] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2013] [Accepted: 01/23/2014] [Indexed: 11/11/2022] Open
Abstract
One of the most important topics in spintronics is spin transport. In this work, spin transport properties of two-dimensional electron gas in AlxGa1-xN/GaN heterostructure were studied by helicity-dependent photocurrent measurements at room temperature. Spin-related photocurrent was detected under normal incidence of a circularly polarized laser with a Gaussian distribution. On one hand, spin polarized electrons excited by the laser generate a diffusive spin polarization current, which leads to a vortex charge current as a result of anomalous circular photogalvanic effect. On the other hand, photo-induced spin polarized electrons driven by a longitudinal electric field give rise to a transverse current via anomalous Hall Effect. Both of these effects originated from the Rashba spin-orbit coupling. By analyzing spin-related photocurrent varied with laser position, the contributions of the two effects were differentiated and the ratio of the spin diffusion coefficient to photo-induced anomalous spin Hall mobility Ds/μs = 0.08 V was extracted at room temperature.
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Dai J, Lu HZ, Yang CL, Shen SQ, Zhang FC, Cui X. Magnetoelectric photocurrent generated by direct interband transitions in InGaAs/InAlAs two-dimensional electron gas. PHYSICAL REVIEW LETTERS 2010; 104:246601. [PMID: 20867319 DOI: 10.1103/physrevlett.104.246601] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/01/2010] [Indexed: 05/29/2023]
Abstract
We report the observation of magnetoelectric photocurrent generated via direct interband transitions in an InGaAs/InAlAs two-dimensional electron gas by a linearly polarized incident light. The electric current is proportional to the in-plane magnetic field, which unbalances the velocities of the photoexcited carriers with opposite spins and consequently generates the electric current from a hidden spin photocurrent. The spin photocurrent can be evaluated from the measured electric current, and the conversion coefficient of spin photocurrent to electric current is self-consistently estimated to be 10(-3)-10(-2) per Tesla. The observed light-polarization dependence of the electric current is well explained by a theoretical model which reveals the wave vector angle dependence of the photoexcited carrier density.
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Affiliation(s)
- Junfeng Dai
- Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China
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21
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Tang CG, Chen YH, Liu Y, Wang ZG. Anomalous-circular photogalvanic effect in a GaAs/AlGaAs two-dimensional electron gas. JOURNAL OF PHYSICS. CONDENSED MATTER : AN INSTITUTE OF PHYSICS JOURNAL 2009; 21:375802. [PMID: 21832354 DOI: 10.1088/0953-8984/21/37/375802] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
We have studied the circular photogalvanic effect (CPGE) in a GaAs/AlGaAs two-dimensional electron gas excited by near infrared light at room temperature. The anomalous CPGE observed under normal incidence indicates a swirling current which is realized by a radial spin current via the reciprocal spin-Hall effect. The anomalous CPGE exhibits a cubic cosine dependence on the incidence angle, which is discussed in line with the above interpretation.
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Affiliation(s)
- C G Tang
- Key Laboratory of Semiconductor Materials Science, Institute of Semiconductors, Chinese Academy of Sciences, PO Box 912, Beijing 100083, People's Republic of China
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