DOCSLIB.ORG

D 5 Spintronics and Emergent Qubits 1

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
D 5 Spintronics and Emergent Qubits 1 D 5 Spintronics and Emergent Qubits 1 Thomas Schapers¨ Peter Grunberg¨ Institut Forschungszentrum Julich¨ GmbH Contents 1 Introduction 2 2 Low dimensional semiconductor systems 2 3 Spin-orbit coupling in semiconductor structures 6 4 Electron interference effects 13 5 Rashba effect in quasi-one-dimensional structures 17 6 Spin-orbit quantum-bits 22 7 Andreev level qubits 29 1Lecture Notes of the 44th IFF Spring School “Quantum Information Processing” (Forschungszentrum Julich,¨ 2013). All rights reserved. D5.2 Thomas Schapers¨ 1 Introduction In this lecture the basic concepts of spintronics will be introduced. The main focus lies on effects related to spin-orbit coupling in semiconductor heterostructures, i.e. the Rashba and Dressel- haus effect. Especially the former allows to control the spin orientation by electrical means. The Rashba effect is essential for the realization of the spin field-effect transistor [1]. By reduc- ing the structure size to one dimension, the properties of spintronic devices can be improved. Here, we will particularly discuss cylindrical semiconductor nanowires, which are prepared by the so-called bottom up approach. By confining the electrons in a gate-defined quantum dot based on semiconductor nanowires, a spin qubits can be realized. It will be discussed, how spin-orbit coupling is employed to manipulate the spin orientation in these qubits. Semicon- ductor nanowires are also very interesting elements to realize Andreev level qubits. Here, the nanowire is used as a normal conducting link between two superconducting electrodes. Owing to phase-coherent Andreev reflection, a Josephson supercurrent can be observed. 2 Low dimensional semiconductor systems InAs-based 2-dimensional electron gases Semiconductor heterostructures based on InAs or its alloys are particularly suited for observing a strong spin-orbit coupling. A typical layer sequence is depicted in Fig. 1(a) [2]. Here, the 2-dimensional electron gas is located in a Ga0:47In0:53As layer at the boundary to the InP spacer layer. The Ga0:47In0:53As semiconductor has a smaller band gap compared to InP. At an indium content of 53% of the GaInAs layer the lattice constant fits to the lattice constant of InP. The electrons in the 2DEG are provided by the n-type doped InP layer which is separated from the 2DEG by a spacer layer (modulation doping). The whole structure is grown on an InP wafer. Heterostructures containing phosphorus are mostly grown by means of metal-organic vapor phase epitaxy (MOVPE). Here, the metal-organic precursors, e.g. trimethylindium (TMIn), trimethylgallium (TMGa), AsH3, or PH3, are added to the carrier gas, i.e. H2 or N2, which flows in a reactor over the surface of the wafer. In Fig. 2 the temperature dependence of the mobility of a 2-dimensional electron gas in an InGaAs/InP heterostructure is shown. Down to temperatures of around 40 K the mobility is limited by phonon scattering. At temperatures below 40 K the mobility saturates, which can be attributed to alloy scattering. Mobilities above 100000 cm2/Vs can be achieved [2]. In contrast to a 2-dimensional electron gas in a GaAs/AlGaAs heterostructures, the electron gas is located in a ternary material, where the In and Ga atoms are statistically distributed in the crystal. The corresponding disorder potential results in an additional scattering contribution, which limits the mobility at low temperatures. A typical conduction band profile of a GaInAs/InP heterostructure with an additional strained Ga0:23In0:77As layer is depicted in Fig. 3. The larger In content of 77% leads to a smaller band gap and a smaller effective electron mass compared to Ga0:47In0:53As. Furthermore, due to the smaller disorder potential the alloy scattering contribution is lowered. As can be seen in Fig. 3, the electron wave function is mainly located in the strained Ga0:23In0:77As layer. Owing to the different barrier materials and the doping at only one side of the Ga0:23In0:77As well, the rectangular quantum well is tilted. The tilted potential profile results in an electric field in the quantum well. The presence of an electric field in the 2-dimensional electron gas is an important prerequisite for the Rashba effect introduced below. Spintronics D5.3 Fig. 1: (a) Layer sequence of a GaInAs/InP heterostructure. The 2DEG is located in the GaInAs layer at the boundary to the InP spacer. (b) Conduction band profile and electron wave func- tions of the 2DEG at the boundary of the GaInAs/InP interface. Fig. 2: Temperature dependence of a 2-dimensional electron gas in a GaInAs/InP heterostruc- ture. At low temperatures the mobility is limited by alloy scattering. D5.4 Thomas Schapers¨ Fig. 3: Conduction band profile and squared amplitude jj2 of the electron wave function in a GaInAs/InP heterstructures with an inserted strained Ga0:23In0:77As layer. By employing etching methods the dimension of 2-dimensional electron gas can be reduced to a 1-dimensional wire structure. The etching process can either be performed by wet chemical etching or by dry etching methods. As described in the next section, a more elegant way is to prepare these wire structures directly by means of epitaxial growth. Semiconductor nanowires Nano-scaled wire structures can also be fabricated by self-organized growth without using elab- orate lithographical means. One possible approach is to use the vapor-liquid-solid (VLS) growth mode [3]. Here, a nanometer-size gold particle is used as a seed particle for the nanowire growth. In many cases InAs is used as a semiconductor material. The underlying reason is that at the surface an electron accumulation layer is formed due to the Fermi level pinning within the conduction band [cf. Fig. 4(a)]. This property is only found in a few semiconductors, e.g. InAs, InN, or InSb. It ensures that even for low nanowire diameters the nanowires contain conductive electrons. For most other semiconductors a depletion layer is formed at the surface, e.g. for GaAs or Si, owing to the Fermi level pinning within the band gap [cf. Fig. 4(b)]. As an alternative to the VLS method, nanowires can also be fabricated by selective-area metal- organic vapor phase epitaxy (SA-MOVPE). Here, a pre-patterned substrate is used, where the nanowires are grown only at those positions where holes are present in a dielectric mask layer. By this method the location of the nanowires can be determined, which is advantageous for subsequent device processing [cf. Fig. 5(b)]. For transport measurements the as-grown nanowires are usually separated from the substrate and transferred to another substrate with alignment markers. By employing electron beam lithography these nanowire are contacted. A scanning electron micrograph of a typical con- tacted semiconductor nanowire is shown in Fig. 5(a). Spintronics D5.5 Fig. 4: (a) Semiconductor nanowire with a surface accumulation layer. (b) Nanowire with a depletion layer at the surface. Fig. 5: (a) Scanning electron beam micrograph of a field of InAs nanowires grown by selective- area MOVPE. (b) InAs nanowire contacted with ohmic contacts on both terminals. In addition, gate fingers are placed in the center, in order to control the electron concentration. D5.6 Thomas Schapers¨ Fig. 6: Schematics of a spin transistor: (a) No gate voltage is applied. The spin precession due to the presence of the Rashba effect leads to a spin orientation which is opposite to the magnetization of the drain electrode. No current can flow in this case, corresponding to a red traffic light. (b) A gate voltage is applied, which enhances the Rashba effect. Owing to stronger spin precession, the spin orientation of the electrons arriving at the drain electrode fits to its magnetization. A current can flow, corresponding to a green traffic light. 3 Spin-orbit coupling in semiconductor structures Spintronics: Basic concept A well-known example of a spintronic device is the spin field-effect transistor. In Fig. 6 a schematics of the spin field-effect transistor is shown [1, 4]. The spin transistor consist of three components: a spin injector as the source electrode, a semiconducting area where the spin orientation is controlled, and a spin detector as the drain electrode. Here, we will focus on the properties of the semiconductor channel located in between the magnetic contacts. In Fig. 6(a) the spin precession in a spin transistor is shown, when no voltage is applied to the gate electrode on top of the semiconductor channel. In the channel the spin is precessing owing to the presence of the Rashba spin-orbit coupling [5]. For the sake of simplicity we assumed that the electron arrives at the drain contact with a spin orientation opposite to the spin orientation in the detector electrode. In this case the electrons cannot enter the detector, since there are no states available the incoming electrons can occupy. As a consequence, the current through the spin transistor is blocked. As will be explained below in detail, by applying a gate voltage the strength of the Rashba spin-orbit coupling can be enhanced. This leads to a stronger spin precession so that the spin orientation of the electrons arriving at the drain electrode fits to the magnetization of the detector electrodes. Now a current can flow in the structure, since the electrons can enter the drain electrode. Below we will explain the physical background of spin-orbit coupling in a semiconductor het- erostructure in detail. Furthermore, a method will be introduced to determine the strength of spin-orbit coupling by transport experiments. Finally, spin-orbit coupling in wire structures will be discussed. Spintronics D5.7 Fig. 7: (a) Schematic illustration of the Rashba spin-orbit coupling in a 2-dimensional electron gas (b) Energy-momentum dispersion with an energy splitting due to the Rashba effect.
Load more

Recommended publications
  • Controlling Spin-Orbit Interactions in Silicon Quantum Dots Using Magnetic Field Direction
    PHYSICAL REVIEW X 9, 021028 (2019) Controlling Spin-Orbit Interactions in Silicon Quantum Dots Using Magnetic Field Direction ‡ Tuomo Tanttu,1,* Bas Hensen,1 Kok Wai Chan,1 Chih Hwan Yang,1 Wister Wei Huang,1 Michael Fogarty,1, Fay Hudson,1 † Kohei Itoh,2 Dimitrie Culcer,3,4 Arne Laucht,1 Andrea Morello,1 and Andrew Dzurak1, 1Center for Quantum Computation and Communication Technology, School of Electrical Engineering and Telecommunications, The University of New South Wales, Sydney, NSW 2052, Australia 2School of Fundamental Science and Technology, Keio University, 3-14-1 Hiyoshi, Kohokuku, Yokohama 223-8522, Japan 3School of Physics, The University of New South Wales, Sydney 2052, Australia 4ARC Centre for Excellence in Future Low-Energy Electronics Technologies, Sydney 2052, Australia (Received 22 October 2018; revised manuscript received 14 February 2019; published 10 May 2019) Silicon quantum dots are considered an excellent platform for spin qubits, partly due to their weak spin-orbit interaction. However, the sharp interfaces in the heterostructures induce a small but significant spin-orbit interaction that degrades the performance of the qubits or, when understood and controlled, could be used as a powerful resource. To understand how to control this interaction, we build a detailed profile of the spin-orbit interaction of a silicon metal-oxide-semiconductor double quantum-dot system. We probe the derivative of the Stark shift, g-factor and g-factor difference for two single-electron quantum-dot qubits as a function of external magnetic field and find that they are dominated by spin-orbit interactions originating from the vector potential, consistent with recent theoretical predictions.
    [Show full text]
  • Absence of the Rashba Effect in Undoped Asymmetric Quantum Wells
    Absence of the Rashba effect in undoped asymmetric quantum wells P.S. Eldridge 1,W.J.H Leyland 2, J.D. Mar 2, P.G. Lagoudakis 1, R. Winkler 3, O.Z. Karimov 1, M. Henini 4, D Taylor 4, R.T. Phillips 2 and R T Harley 1 1 School of Physics and Astronomy, University of Southampton, Southampton, SO17 IBJ, UK 2 Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, UK 3 Department of Physics, Northern Illinois University, DeKalb, IL 60115, USA 4 School of Physics and Astronomy, University of Nottingham, Nottingham NG7 4RD, UK To an electron moving in free space an electric field appears as a magnetic field which interacts with and can reorient the electron’s spin. In semiconductor quantum wells this spin- orbit interaction seems to offer the possibility of gate-voltage control in spintronic devices but, as the electrons are subject to both ion-core and macroscopic structural potentials, this over-simple picture has lead to intense debate. For example, an externally applied field acting on the envelope of the electron wavefunction determined by the macroscopic potential, underestimates the experimentally observed spin-orbit field by many orders of magnitude while Ehrenfest’s theorem suggests that it should actually be zero. Here we challenge, both experimentally and theoretically, the widely held belief that any inversion asymmetry of the macroscopic potential, not only electric field, will produce a significant spin-orbit field for electrons. This conclusion has far-reaching consequences for the design of spintronic devices while illuminating important fundamental physics. Spin-orbit splittings induced by applied electric field in semiconductor heterostructures in principle enable a new generation of spintronic devices where electron spin is manipulated by external gate voltage.
    [Show full text]
  • Rashba Spin-Orbit Interaction in Semiconductor Nanostructures (Review)
    Asian Journal of Physical and Chemical Sciences 8(2): 32-44, 2020; Article no.AJOPACS.57016 ISSN: 2456-7779 Rashba Spin-orbit Interaction in Semiconductor Nanostructures (Review) Ibragimov Behbud Guseyn1* 1Institute of Physics, Azerbaijan National Academy of Sciences, Azerbaijan State Oil and Industry University, Azerbaijan. Author’s contribution The sole author designed, analysed, interpreted and prepared the manuscript. Article Information DOI: 10.9734/AJOPACS/2020/v8i230115 Editor(s): (1) Dr. Thomas F. George, University of Missouri - St. Louis One University Boulevard St. Louis, USA. (2) Dr. Shridhar N. Mathad, KLE Institute of Technology, India. Reviewers: (1) Kruchinin Sergei, Ukraine. (2) Subramaniam Jahanadan, Malaysia. (3) M. Abu-Shady, Menoufia University, Egypt. (4) Vinod Prasad, India. (5) Ricardo Luís Lima Vitória, Universidade Federal do Pará, Brazil. Complete Peer review History: http://www.sdiarticle4.com/review-history/57016 Received 25 March 2020 Accepted 01 June 2020 Review Article Published 09 June 2020 ABSTRACT In this work I review of the theoretical and experimental issue related to the Rashba Spin-Orbit interaction in semiconductor nanostructures. The Rashba spin-orbit interaction has been a promising candidate for controlling the spin of electrons in the field of semiconductor spintronics. In this work, I focus study of the electrons spin and holes in isolated semiconductor quantum dots and rings in the presence of magnetic fields. Spin-dependent thermodynamic properties with strong spin- orbit coupling inside their band structure in systems are investigated in this work. Additionally, specific heat and magnetization in two dimensional, one-dimensional quantum ring and dot nanostructures with Spin Orbit Interaction are discussed. Keywords: Spin-orbit interaction; Rashba effect; two dimension electron gas; one-dimensional ring; quantum wire; quantum dot; semiconductor nanostructures.
    [Show full text]
  • Rashba Spin-Orbit Interaction in 1-Dimensional Nanowires
    Rashba spin-orbit interaction in 1-dimensional nanowires Damaz de Jong December 16, 2015 Abstract Now that the first signatures of Majorana zero modes have been ob- served in experiments, a huge effort towards topological quantum com- putation is currently underway. Majorana zero modes can appear in nanowire systems, with their topological protection depending on the spin- orbit interaction strength. The spin-orbit interaction strength is therefore a crucial parameter in this experimental field. The largest contribution is expected to be Rashba spin-orbit interaction, which is the subject of this thesis. Spin orbit interaction in semiconducting systems is governed by sym- metry. Spin-orbit interaction is forbidden by symmetry if no additional symmetries are broken in [111] InSb nanowires. Upon reducing the spa- tial symmetry group, both Dresselhaus and Rashba spin-orbit interaction can emerge in the system. In this thesis a perturbative model for Rashba spin-orbit interaction, which occurs when an electric field reduces spatial symmetry, is developed to predict the interaction strength. This model is then compared to numerical simulations in quantum well systems per- formed with Mathematica and in nanowire simulations performed with Kwant. The model, incorporating the effect of changing geometric dimensions, subband number and the material, shows good agreement with the numer- ical simulations. Electrical fields resulting from Schr¨odinger-Poisson sim- ulations are then used to induce Rashba spin-orbit interaction in hexago- nal nanowire systems similar to experimental devices again matching the model. Finally, it is shown that the model can be used to calculate re- sults which are intractable to calculate via numerical simulations to find the effect of superconducting coverage of the nanowire on the spin-orbit interaction.
    [Show full text]
  • Giant Magnetic Band Gap in the Rashba-Split Surface State Of
    www.nature.com/scientificreports OPEN Giant Magnetic Band Gap in the Rashba-Split Surface State of Vanadium-Doped BiTeI: A Received: 7 February 2017 Accepted: 28 April 2017 Combined Photoemission and Ab Published: xx xx xxxx Initio Study I. I. Klimovskikh 1, A. M. Shikin1, M. M. Otrokov1,2,3, A. Ernst8,10, I. P. Rusinov1,2, O. E. Tereshchenko1,5,6, V. A. Golyashov1,5, J. Sánchez-Barriga 9, A. Yu. Varykhalov9, O. Rader9, K. A. Kokh1,6,7 & E. V. Chulkov1,2,3,4 One of the most promising platforms for spintronics and topological quantum computation is the two- dimensional electron gas (2DEG) with strong spin-orbit interaction and out-of-plane ferromagnetism. In proximity to an s-wave superconductor, such 2DEG may be driven into a topologically non-trivial superconducting phase, predicted to support zero-energy Majorana fermion modes. Using angle- resolved photoemission spectroscopy and ab initio calculations, we study the 2DEG at the surface of the vanadium-doped polar semiconductor with a giant Rashba-type splitting, BiTeI. We show that the vanadium-induced magnetization in the 2DEG breaks time-reversal symmetry, lifting Kramers degeneracy of the Rashba-split surface state at the Brillouin zone center via formation of a huge gap of about 90 meV. As a result, the constant energy contour inside the gap consists of only one circle with spin-momentum locking. These findings reveal a great potential of the magnetically-doped semiconductors with a giant Rashba-type splitting for realization of novel states of matter. Two-dimensional electron systems have been attracting the researchers interest for many years due to a number of unique electronic effects.
    [Show full text]
  • Towards the Manipulation of Topological States of Matter
    Towards the manipulation of topological states of matter: A perspective from electron transport Cheng Zhang1,2, Hai-Zhou Lu3,4, Shun-Qing Shen5, Yong P. Chen6,7,8 and Faxian Xiu1,2,9* 1State Key Laboratory of Surface Physics and Department of Physics, Fudan University, Shanghai 200433, China 2Collaborative Innovation Center of Advanced Microstructures, Nanjing 210093, China 3Institute for Quantum Science and Engineering and Department of Physics, South University of Science and Technology of China, Shenzhen 518055, China 4Shenzhen Key Laboratory of Quantum Science and Engineering, Shenzhen 518055, China 5Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China 6Department of Physics and Astronomy, Purdue University, West Lafayette, Indiana 47907, USA 7Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA 8School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907, USA 9Institute for Nanoelectronic Devices and Quantum Computing, Fudan University, Shanghai 200433, China *Corresponding author: Faxian Xiu, E-mail: [email protected] 1 / 39 Abstract The introduction of topological invariants, ranging from insulators to metals, has provided new insights into the traditional classification of electronic states in condensed matter physics. A sudden change in the topological invariant at the boundary of a topological nontrivial system leads to the formation of exotic surface states that are dramatically different from its bulk. In recent years, significant advancements in the exploration of the physical properties of these topological systems and regarding device research related to spintronics and quantum computation have been made. Here, we review the progress of the characterization and manipulation of topological phases from the electron transport perspective and also the intriguing chiral/Majorana states that stem from them.
    [Show full text]
  • New Perspectives for Rashba Spin-Orbit Coupling
    New Perspectives for Rashba Spin-Orbit Coupling A. Manchon1, H.C. Koo2,3, J. Nitta4, S.M. Frolov5, R.A. Duine6 1King Abdullah University of Science and Technology (KAUST), Physical Science and Engineering Division, Thuwal 23955-6900, Saudi Arabia 2Center for Spintronics Research, Korea Institute of Science and Technology (KIST), 39-1 Hawolgok-dong, Seongbukgu, Seoul, 136-791, Korea 3KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, 136-701, Korea 4Department of Materials Science, Tohoku University, 980-8579 Sendai, Miyagi, Japan 5Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA, 15260, USA 6Institute for Theoretical Physics and Center for Extreme Matter and Emergent Phenomena, Utrecht University, Leuvenlaan 4, 3584 CE Utrecht, The Netherlands In 1984, Bychkov and Rashba introduced a simple form of spin-orbit coupling to explain certain peculiarities in the electron spin resonance of two-dimensional semiconductors. Over the past thirty years, similar ideas have been leading to a vast number of predictions, discoveries, and innovative concepts far beyond semiconductors. The past decade has been particularly creative with the realizations of means to manipulate spin orientation by moving electrons in space, controlling electron trajectories using spin as a steering wheel, and with the discovery of new topological classes of materials. These developments reinvigorated the interest of physicists and materials scientists in the development of inversion asymmetric structures ranging from layered graphene-like materials to cold atoms. This review presents the most remarkable recent and ongoing realizations of Rashba physics in condensed matter and beyond. 0 Introduction In crystals lacking an inversion center, electronic energy bands are split by spin-orbit (SO) coupling.
    [Show full text]
  • Majorana States in Ferromagnetic Shiba Chains
    Master's Thesis Theoretical Physics Majorana states in ferromagnetic Shiba chains Kim P¨oyh¨onen 2015 Supervisor: Dr. Teemu Ojanen Examiners: Dr. Teemu Ojanen Prof. Kai Nordlund HELSINKI UNIVERSITY DEPARTMENT OF PHYSICS P.O. Box 64 (Gustaf H¨allstr¨omin katu 2) 00014 University of Helsinki HELSINGIN YLIOPISTO – HELSINGFORS UNIVERSITET – UNIVERSITY OF HELSINKI Tiedekunta/Osasto – Fakultet/Sektion – Faculty/Section Laitos – Institution – Department Faculty of Science Department of Physics Tekijä – Författare – Author Kim Pöyhönen Työn nimi – Arbetets titel – Title Majorana states in ferromagnetic Shiba chains Oppiaine – Läroämne – Subject Theoretical Physics Työn laji – Arbetets art – Level Aika – Datum – Month and year Sivumäärä – Sidoantal – Number of pages M. Sc. Thesis August 2011 64 Tiivistelmä – Referat – Abstract Topological superconductors, combining the principles of topology and condensed-matter physics, are a new field which has seen much progress in the past two decades. In particular, they are theorized to support Majorana bound states, a type of quasiparticle with several interesting properties – most notably, they exhibit nonabelian exchange statistics, which has applications in fault tolerant quantum computing. During the past few years, several groups have observed effects in topological superconductors indicating that an experimental confirmation of their existence may be imminent. Recently experimental focus has been on ferromagnetic systems with spin-orbit coupling, serving as the motivation for our research. In this thesis, we study the topological properties of a system consisting of magnetic adatoms implanted on a two-dimensional superconducting substrate with Rashba spin-orbit coupling. Starting from the mean-field Bogoliubov-de Gennes Hamiltonian, we derive a nonlinear eigenvalue problem describing the system, generalizing previous results which considered a linearized version.
    [Show full text]
  • Giant Magnetic Band Gap in the Rashba-Split
    www.nature.com/scientificreports OPEN Giant Magnetic Band Gap in the Rashba-Split Surface State of Vanadium-Doped BiTeI: A Received: 7 February 2017 Accepted: 28 April 2017 Combined Photoemission and Ab Published: xx xx xxxx Initio Study I. I. Klimovskikh 1, A. M. Shikin1, M. M. Otrokov1,2,3, A. Ernst8,10, I. P. Rusinov1,2, O. E. Tereshchenko1,5,6, V. A. Golyashov1,5, J. Sánchez-Barriga 9, A. Yu. Varykhalov9, O. Rader9, K. A. Kokh1,6,7 & E. V. Chulkov1,2,3,4 One of the most promising platforms for spintronics and topological quantum computation is the two- dimensional electron gas (2DEG) with strong spin-orbit interaction and out-of-plane ferromagnetism. In proximity to an s-wave superconductor, such 2DEG may be driven into a topologically non-trivial superconducting phase, predicted to support zero-energy Majorana fermion modes. Using angle- resolved photoemission spectroscopy and ab initio calculations, we study the 2DEG at the surface of the vanadium-doped polar semiconductor with a giant Rashba-type splitting, BiTeI. We show that the vanadium-induced magnetization in the 2DEG breaks time-reversal symmetry, lifting Kramers degeneracy of the Rashba-split surface state at the Brillouin zone center via formation of a huge gap of about 90 meV. As a result, the constant energy contour inside the gap consists of only one circle with spin-momentum locking. These findings reveal a great potential of the magnetically-doped semiconductors with a giant Rashba-type splitting for realization of novel states of matter. Two-dimensional electron systems have been attracting the researchers interest for many years due to a number of unique electronic effects.
    [Show full text]
  • Anomalous Rashba Effect of Bi Thin Film Studied by Spin-Resolved ARPES 79 Applicable to Advanced Spintronic Devices [2, 5, 6]
    ProvisionalChapter chapter 5 Anomalous Rashba Effect ofof BiBi ThinThin FilmFilm StudiedStudied by Spin-Resolved ARPES by Spin-Resolved ARPES Akari Takayama Akari Takayama Additional information is available at the end of the chapter Additional information is available at the end of the chapter http://dx.doi.org/10.5772/66278 Abstract The Rashba effect is a momentum‐dependent splitting of spin bands in two‐dimen‐ sional systems such as surface, interface and heterostructure. The effect is caused by broken space‐inversion symmetry and spin‐orbit coupling and allows to manipulate and generate the spin by the electric fields, that is, without the magnetic field. It means that the devices applied to the Rashba effect have many advantages. Bismuth is known as a promising candidate to investigate the surface Rashba effect, and the spin struc ‐ ture of Bi surface has also been intensively discussed. However, it is unclear to what extent the so far believed simple vortical spin structure is adequate. To understand the surface properties of the Rashba system is particularly important when utilizing the Rashba effect to the spintronic devices, since it is desirable to control the spin polariza ‐ tion when developing new types of devices. In this chapter, we report that the surface spin states of the Bi thin film exhibit unusual characteristics unlike the conventional Rashba splitting by using a spin‐ and angle‐resolved photoemission spectroscopy measurement. Keywords: Rashba effect, spin‐resolved ARPES, thin film, bismuth 1. Introduction As we know and use, spintronic devices to use a spin‐polarized electrons have actualized. The magnetic storage technology uses giant magneto‐resistance [1].
    [Show full text]
  • Spin-Orbit Coupling and Strong Correlations in Ultracold Bose Gases
    Spin-orbit coupling and strong correlations in ultracold Bose gases DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By William S. Cole, Jr., B.S. Graduate Program in Physics The Ohio State University 2014 Dissertation Committee: Professor Nandini Trivedi, Advisor Professor Mohit Randeria Professor P. Chris Hammel Professor Richard J. Furnstahl c Copyright by William S. Cole, Jr. 2014 Abstract The ability to create artificial gauge fields for neutral atoms adds a powerful new dimension to the idea of using ultracold atomic gases as \quantum simulators" of models that arise in conventional solid state physics. At present, cold atom experiments are able to simulate orbital magnetism and a certain kind of spin-orbit coupling at scales which are quite difficult to achieve in the solid state. This takes us beyond the realm of simulation into questions about new states of matter which might only be possible in cold atom experiments. Indeed, as a byproduct of finding methods to simulate traditional gauge potentials for neutral gases, it has been realized that gauge potentials with no solid state analog can also be created and finely tuned to manipulate the few- and many-body physics of bosons and fermions in remarkable new ways. Motivated along these lines, in this dissertation I address several issues related to bosons with spin-orbit coupling. After an introduction to synthetic gauge fields in general I describe Rashba spin-orbit coupling specifically and how it modifies the usual behavior of bosons in the continuum and in a harmonic trapping potential.
    [Show full text]
  • Origin of Rashba Spin-Splitting and Strain Tunability in Ferroelectric Bulk
    pubs.acs.org/JPCL Letter Origin of Rashba Spin Splitting and Strain Tunability in Ferroelectric Bulk CsPbF3 Preeti Bhumla,* Deepika Gill, Sajjan Sheoran, and Saswata Bhattacharya* Cite This: J. Phys. Chem. Lett. 2021, 12, 9539−9546 Read Online ACCESS Metrics & More Article Recommendations *sı Supporting Information ABSTRACT: Spin−orbit coupling (SOC) in conjunction with broken inversion symmetry acts as a key ingredient for several intriguing quantum phenomena, viz., Rashba−Dresselhaus (RD) effect. The coexistence of spontaneous polarization and the RD effect in ferroelectric (FE) materials enables the electrical control of spin degrees of freedom. Here, we explore the fi FE lead halide perovskite CsPbF3 as a potential candidate in the eld of spintronics by employing state-of-the-art first-principles-based methodologies, viz., density functional theory (DFT) with semilocal and hybrid functional (HSE06) combined with SOC and many-body perturbation theory (G0W0). For a deeper understanding of the observed spin splitting, the spin textures are analyzed using the k.p model Hamiltonian. We find there is no out-of-plane spin component indicating that the Rashba splitting dominates over Dresselhaus splitting. We also observe that the strength of Rashba spin splitting can be substantially tuned on application of uniaxial strain (±5%). More interestingly, we notice reversible spin textures by switching the FE polarization in CsPbF3 perovskite, making it potent for perovskite-based spintronic applications. ead halide perovskites have evolved as an excellent choice studied as promising functional materials for spin-based − in optoelectronics owing to their exotic properties, viz., applications.29 33 Recently, a significant Rashba effect has L ffi suitable optical band gap, high absorption coe cient, low trap been reported in the tetragonal phase of MAPbI3 (MA = 1−9 + 34,35 ff density, and reasonable manufacturing cost.
    [Show full text]