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rashba electron transport in one-dimensional quantum waveguides

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Science China(Physics,Mechanics & Astronomy) 2010年第1期53卷 16-23页

作者： LIU DuanYang 1 , XIA JianBai 1,2 & CHANG YiaChung 2 1 State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Beijing 100083, China 2 Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan 11529, China State Key Laboratory for Superlattices and Microstructures Institute of Semiconductors Beijing China Research Center for Applied Sciences Academia Sinica Taipei Taiwan China

The properties of rashba wave function in the planar one-dimensional waveguide are studied, and the following results are obtained. Due to the rashba effect, the plane waves of electron with the energy E divide into two kinds of waves with the wave vectors k 1 =k 0 +k δ and k 2 =k 0 -k δ , where k δ is proportional to the rashba coefficient, and their spin orientations are +π/2 (spin up) and -π/2 (spin down) with respect to the circuit, respectively. If there is gate or ferromagnetic contact in the circuit, the rashba wave function becomes standing wave form exp(±ik δ l)sin[k 0 (l-L)], where L is the position coordinate of the gate or contact. Unlike the electron without considering the spin, the phase of the rashba plane or standing wave function depends on the direction angle θ of the circuit. The travel velocity of the rashba waves with the wave vector k 1 or k 2 are the same hk0/m * . The boundary conditions of the rashba wave functions at the intersection of circuits are given from the continuity of wave functions and the conservation of current density. Using the boundary conditions of rashba wave functions we study the transmission and reflection probabilities of rashba electron moving in several structures, and find the interference effects of the two rashba waves with different wave vectors caused by ferromagnetic contact or the gate. Lastly we derive the general theory of multiple branches structure. The theory can be used to design various spin polarized devices.

关键词： rashba wave function one-dimensional waveguide boundary condition

Crossover from 2D metal to 3D Dirac semimetal in metallic PtTe2 films with local rashba effect

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Science Bulletin 2019年第15期64卷 1044-1048页

作者： Ke Deng Mingzhe Yan Chu-Ping Yu Jiaheng Li Xue Zhou Kenan Zhang Yuxin Zhao Koji Miyamoto Taichi Okuda Wenhui Duan Yang Wu Xiaoyan Zhong Shuyun Zhou State Key Laboratory of Low Dimensional Quantum Physics and Department of Physics Tsinghua UniversityBeijing100084China National Center for Electron Microscopy in Beijing Key Laboratory of Advanced Materials(MOE)State Key Laboratory of New Ceramics and Fine ProcessingSchool of Materials Science and EngineeringTsinghua UniversityBeijing100084China Hiroshima Synchrotron Radiation Center Hiroshima UniversityHigashi-Hiroshima739-0046Japan Collaborative Innovation Center of Quantum Matter Beijing100084China Department of Physics and Tsinghua-Foxconn Nanotechnology Research Center Tsinghua UniversityBeijing100084China

PtTe2 and PtSe2 with trigonal structure have attracted extensive research interests since the discovery of type-II Dirac fermions in the bulk crystals. The evolution of the electronic structure from bulk 3D topological semimetal to 2D atomic thin films is an important scientific question. While a transition from 3D type-II Dirac semimetal in the bulk to 2D semiconductor in monolayer(ML) film has been reported for PtSe2, so far the evolution of electronic structure of atomically thin PtTe2 films still remains unexplored.Here we report a systematic angle-resolved photoemission spectroscopy(ARPES) study of the electronic structure of high quality PtTe2 films grown by molecular beam epitaxy with thickness from 2 ML to 6 ML.ARPES measurements show that PtTe2 films still remain metallic even down to 2 ML thickness, which is in sharp contrast to the semiconducting property of few layer PtSe2 films. Moreover, a transition from 2D metal to 3D type-II Dirac semimetal occurs at film thickness of 4–6 ML. In addition, Spin-ARPES measurements reveal helical spin textures induced by local rashba effect in the bulk PtTe2 crystal, suggesting that similar hidden spin is also expected in few monolayer PtTe2 films. Our work reveals the transition from2D metal to 3D topological semimetal and provides new opportunities for investigating metallic 2D films with local rashba effect.

关键词： PtTe2 Dirac semimetal Local rashba effect Topological semimetal Topological superconductivity

Spin-Polarized Currents in Double Quantum Dots with rashba Spin-Orbit Interactions

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Chinese Physics Letters 2013年第8期30卷 132-135页

作者：李振山潘晖吕嵘 Department of Physics and State Key Laboratory of Software Development Environment Beihang UniversityBeijing 100191 Department of Physics Tsinghua UniversityBeijing 100084

We propose a new scheme of realizing spin-polarized currents in a double quantum dot system.In the presence of rashba spin-orbit coupling interactions and different Zeeman splittings of each quantum dot,the currents are spin-polarized.The polarization can be controlled by tuning the strength of rashba spin-orbit coupling and external magnetic fields,which can produce nearly 100%spin-polarized currents.Furthermore,we explain and analyze the mechanism of the strongly spin-polarized currents.Lastly we give two phase diagrams to display our results.

关键词： polarized quantum rashba

Wide-range ideal 2D rashba electron gas with large spin splitting in Bi_(2)Se_(3)/MoTe_(2) heterostructure

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npj Computational Materials 2017年第1期3卷 442-447页

作者： Te-Hsien Wang Horng-Tay Jeng Department of Physics National Tsing Hua UniversityHsinchu 30013Taiwan

An application-expected ideal two-dimensional rashba electron gas,i.e.,nearly all the conduction electrons occupy the rashba bands,is crucial for semiconductor spintronic applications.We demonstrate that such an ideal two-dimensional rashba electron gas with a large rashba splitting can be realized in a topological insulator Bi_(2)Se_(3) ultrathin film grown on a transition metal dichalcogenides MoTe_(2) substrate through first-principle calculations.Our results show the rashba bands exclusively over a very large energy interval of about 0.6 eV around the Fermi level within the MoTe2 semiconducting gap.Such a wide-range ideal twodimensional rashba electron gas with a large spin splitting,which is desirable for real devices utilizing the rashba effect,has never been found before.Due to the strong spin-orbit coupling,the strength of the rashba splitting is comparable with that of the heavy-metal surfaces such as Au and Bi surfaces,giving rise to a spin precession length as small as~10 nm.The maximum in-plane spin polarization of the inner(outer)rashba band near theΓpoint is about 70%(60%).The room-temperature coherence length is at least several times longer than the spin precession length,providing good coherency through the spin processing devices.The wide energy window for ideal rashba bands,small spin precession length,as well as long spin coherence length in this twodimensional topological insulator/transition metal dichalcogenides heterostructure pave the way for realizing an ultrathin nanoscale spintronic device such as the Datta-Das spin transistor at room-temperature.

关键词： temperature. splitting rashba

Spin Hall effect in prototype rashba ferroelectrics GeTe and SnTe

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npj Computational Materials 2020年第1期6卷 1607-1613页

作者： Haihang Wang Priya Gopal Silvia Picozzi Stefano Curtarolo Marco Buongiorno Nardelli Jagoda Sławińska Department of Physics University of North TexasDentonTX 76203USA Consiglio Nazionale delle Ricerche Istituto SPINUOS L’AquilaSede di lavoro CNR-SPIN c/o Univ.G.D’Annunzio66100 ChietiItaly Center for Autonomous Materials Design Duke UniversityDurhamNC 27708USA Materials Science Electrical EngineeringPhysics and ChemistryDuke UniversityDurhamNC 27708USA

Ferroelectric rashba semiconductors(FERSCs)have recently emerged as a promising class of spintronics materials.The peculiar coupling between spin and polar degrees of freedom responsible for several exceptional properties,including ferroelectric switching of rashba spin texture,suggests that the electron’s spin could be controlled by using only electric fields.In this regard,recent experimental studies revealing charge-to-spin interconversion phenomena in two prototypical FERSCs,GeTe and SnTe,appear extremely relevant.Here,by employing density functional theory calculations,we investigate spin Hall effect(SHE)in these materials and show that it can be large either in ferroelectric or paraelectric structure.We further explore the compatibility between doping required for the practical realization of SHE in semiconductors and polar distortions which determine rashba-related phenomena in FERSCs,but which could be suppressed by free charge carriers.

关键词： structure rashba ferroelectric

Defect-mediated rashba engineering for optimizing electrical transport in thermoelectric BiTeI

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npj Computational Materials 2020年第1期6卷 774-780页

作者： Xin Li Ye Sheng Lihua Wu Shunbo Hu Jiong Yang David J.Singh Jihui Yang Wenqing Zhang Materials Genome Institute Shanghai University99 Shangda Road200444 ShanghaiChina Materials Science and Engineering Department University of WashingtonSeattleWA 98195USA Department of Physics and Astronomy and Department of Chemistry University of MissouriColumbiaMO 65211USA Department of Physics and Shenzhen Institute for Quantum Science&Technology Southern University of Science and Technology518055 ShenzhenGuangdongChina Guangdong Provincial Key Laboratory of Computational Science and Material Design and Shenzhen Key Laboratory of Advanced Quantum Functional Materials and DevicesSouthern University of Science and Technology518055 ShenzhenGuangdongChina

The rashba effect plays a vital role in electronic structures and related functional properties.The strength of the rashba effect can be measured by the rashba parameter α_(R);it is desirable to manipulate α_(R) to control the functional properties.The current work illustrates how α_(R) can be systematically tuned by doping,taking BiTeI as an example.

关键词： properties rashba doping

金属表面rashba自旋轨道耦合作用研究进展

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物理学报 2015年第18期64卷 103-119页

作者：龚士静段纯刚华东师范大学、信息科学技术学院极化材料与器件教育部重点实验室上海200241

自旋轨道耦合是电子自旋与轨道相互作用的桥梁,它提供了利用外电场来调控电子的轨道运动、进而调控电子自旋状态的可能.固体材料中有很多有趣的物理现象,例如磁晶各向异性、自旋霍尔效应、拓扑绝缘体等,都与自旋轨道耦合密切相关.在表面... 详细信息

自旋轨道耦合是电子自旋与轨道相互作用的桥梁,它提供了利用外电场来调控电子的轨道运动、进而调控电子自旋状态的可能.固体材料中有很多有趣的物理现象,例如磁晶各向异性、自旋霍尔效应、拓扑绝缘体等,都与自旋轨道耦合密切相关.在表面/界面体系中,由于结构反演不对称导致的自旋轨道耦合称为rashba自旋轨道耦合,它最早在半导体材料中获得研究,并因其强度可由栅电压灵活调控而备受关注,成为电控磁性的重要物理基础之一.继半导体材料后,金属表面成为具有rashba自旋轨道耦合作用的又一主流体系.本文以Au(111),Bi(111),Gd(0001)等为例综述了磁性与非磁性金属表面rashba自旋轨道耦合的研究进展,讨论了表面电势梯度、原子序数、表面态波函数的对称性,以及表面态中轨道杂化等因素对金属表面rashba自旋轨道耦合强度的影响.在磁性金属表面,同时存在rashba自旋轨道耦合作用与磁交换作用,通过rashba自旋轨道耦合可能实现电场对磁性的调控.最后,阐述了外加电场和表面吸附等方法对金属表面rashba自旋轨道耦合的调控.基于密度泛函理论的第一性原理计算和角分辨光电子能谱测量是金属表面rashba自旋轨道耦合的两大主要研究方法,本文综述了这两方面的研究结果,对金属表面rashba自旋轨道耦合进行了深入全面的总结和分析.

关键词： rashba 自旋轨道耦合金属表面角分辨率光电子能谱

A New Method to Calculate the rashba Spin Splitting in Ⅲ-Nitride Heterostructures

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Chinese Physics Letters 2012年第12期29卷 172-176页

作者：李明孙刚范丽波 College of Electrical and Information Engineering Xuchang UniversityXuchang 461000

By constructing proper basis functions,the Kane Hamiltonian is transformed to two separate Hamiltonians,and the Schr?dinger equation for conduction-band envelope functions can be obtained by eliminating the valence band components of the envelope functions.Then we decouple the up-spin and down-spin states and derive the expression for the rashba coefficient and single-particle energy,considering the spin-orbit coupling and the nonparabolicity corrections.Finally,we calculate the rashba spin splitting for Al_(x)Ga_(1-x)N/GaN heterostructures by using the variational method.The rashba spin splitting calculated here is of the same order of magnitude as in other Ⅲ-Ⅴ materials,showing that the internal electric field caused by the high concentration of the 2DEG is crucial for considerable rashba spin splitting.

关键词： rashba Hamiltonian envelope

Electric Field Control of Interface Related Spin Splitting in Step Quantum Wells

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Chinese Physics Letters 2009年第7期26卷 263-266页

作者：郝亚非陈涌海郝国栋王占国 Key Laboratory of Semiconductor Materials Science Institute of Semiconductors Chinese Academy of Sciences PO Box 912 Beijing 100083

Spin splitting of the Aly Ga1-y As/GaAs/A1x Ga1-x As/A1-y Ga1-y As （x ≠ y） step quantum wells （ Q Ws） has been theoretically investigated with a model that includes both the interface and the external electric field contribution. The overall spin splitting is mainly determined by the interface contribution, which can be well manipulated by the external electric field. In the absence of the electric field, the rashba effect exists due to the internal structure inversion asymmetry （SIA）. The electric field can strengthen or suppress the internal SIA, resulting in an increase or decrease of the spin splitting. The step QW, which results in large spin splitting, has advantages in applications to spintronic devices compared with symmetrical and asymmetrical QWs. Due to the special structure design, the spin splitting does not change with the external electric field.

关键词： CONDUCTION SUBBANDS INVERSION ASYMMETRY HETEROSTRUCTURES rashba LAYERS INAS