Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session L36: Spin-Orbitronics in Semiconductor, Topological, and 2D Materials IIFocus Live
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Denis Candido, Univ of Iowa |
Wednesday, March 17, 2021 8:00AM - 8:12AM Live |
L36.00001: Spin-phonon relaxation of Silicene and Germanene from first-principles density-matrix dynamics Hiroyuki Takenaka, Junqing Xu, Ravishankar Sundararaman, Yuan Ping Spin relaxation and decoherence due to coupling with lattice environment is of key importance to quantum information science and spintronics applications. Graphene (GR) has been one of the most popular spintronic materials with the long spin lifetime. Silicene or germanene has a similar Dirac cone linear dispersion to GR, but with larger spin-orbit coupling (SOC) and buckled structure, which exhibits properties of valleytronics and topological insulators. Here, we investigate spin relaxation of silicene and germanene with ab-initio density matrix dynamics with SOC and electron-phonon couplings. We find large spin lifetime anisotropy of two systems compared to GR. Under electric field, we found both the in-plane and out-of-plane spin lifetime strongly decreased, with spin lifetime anisotropy rather unchanged. In addition, the in-plane spin lifetime has weak temperature dependence, in sharp contrast to the out-of-plane one. The dominant electron-phonon coupling for spin relaxation changes from intravalley relaxation at low temperature to intervalley relaxation at high temperature, distinct from GR. Our ab-initio work provides unbiased insights to spin relaxation mechanism of topological 2D materials. |
Wednesday, March 17, 2021 8:12AM - 8:24AM Live |
L36.00002: Layer- and Gate-tunable Spin-Orbit Coupling in a 2D semiconductor
probed by Shubnikov-de Haas Oscillations. Dmitry Shcherbakov, Petr Stepanov, Shahriar Memaran, Yaxian Wang, Yan Xin, Jiawei Yang, Kaya Wei, Ryan Baumbach, Wenkai Zheng, Kenji Watanabe, Takashi Taniguchi, Marc Bockrath, Dmitry Smirnov, Theo Siegrist, Wolfgang E Windl, Luis Balicas, Chun Ning Lau In semiconductors spin degeneracy can be lifted by breaking time reversal symmetry or by spin-orbit coupling (SOC) when inversion symmetry is broken. We utilize tunability of ultrathin field-effect transistors combined with high mobility of indium selenide (InSe) to demonstrate SOC and to vary it over an unprecendently wide range by breaking the inversion symmetry with out-of-plane electric field. In addition, we demonstrate dependence of parameters of SOC on the number of InSe layers. High accuracy is achieved by the experimental technique: measurement of beating patterns in Shubnikov-de Haas oscillations. We achieve tuning of spin splitting from 0 and 20 meV. However, this is not the limit, as some devices demonstrate an order of magnintude higher SOC, suggesting additional paths of manipulation. |
Wednesday, March 17, 2021 8:24AM - 8:36AM Live |
L36.00003: Spin Nernst effect in a topological insulator Bi2Se3 Rakshit Jain, ARNAB BOSE, Anthony R. Richardella, Timothy S Pillsbury, Yongxi Ou, Nitin Samarth, Robert Alan Buhrman, Daniel C Ralph
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Wednesday, March 17, 2021 8:36AM - 8:48AM Live |
L36.00004: Spin textures in a silver sulfide proustite Sean Koyama, James M Rondinelli Nonmagnetic materials exhibiting spin-orbit coupling (SOC) and broken inversion symmetry have been shown to exhibit spin properties conducive to spintronics applications by exploiting spin textures in momentum space. In this talk, I will present a first-principles electronic structure study of proustite, a polar Ag3AsS3 sulfide, and related A3BQ3 chalcogenides. I will discuss how changes in local atomic structure and orbital hybridization influence the band gaps, band dispersions, and spin-momentum locking at different positions in momentum space in the material family. |
Wednesday, March 17, 2021 8:48AM - 9:00AM Live |
L36.00005: Observation a Chiral Electronic Continuum in the Giant Rashba Spin-Split System, BiTeI Alexander Lee, Bo Peng, Kai Du, Hsiang-Hsi Kung, Bartomeu Monserrat, Sang-Wook Cheong, Girsh Blumberg In BiTeI, the Rashba spin-orbit interaction spin-splits the electronic dispersion in the bulk of the material. The conduction bands cross the Fermi energy leading to a continuum of electronic excitations between spin-polarized sub-bands called the “Rashba continuum.” In our study, we used polarization-resolved Raman scattering to probe the Rashba continuum. We discovered that the continuum appears in the pseudovector symmetry channel, providing direct experimental evidence that the excitations possess chiral symmetry. The lineshape of the continuum is strongly dependent on the incident photon energy. We ran simulations of the resonant Raman scattering spectra for the Rashba continuum using a 3-band model. The calculations of resonant inter-band transitions closely reproduce the lineshape of the chiral Raman signal. |
Wednesday, March 17, 2021 9:00AM - 9:12AM Live |
L36.00006: First-principles study on Giant Hidden Rashba Effects in novel Two-Dimensional Si2Bi2 Seungjun Lee, Young-Kyun Kwon In contrast to the general view in spin-orbit interaction, it was reported that even in materials with centrosymmetry may have hidden Rashba spin-orbit coupling (the R-2 effect) resulting in spatial spin splitting. However, not only its underlying fundamental physics been still unclear, but the search for materials exhibiting the R-2 interaction has also been very limited. Here, through first-principles density functional theory and model Hamiltonian calculations, we investigate giant spin-layer locking observed in novel two-dimensional materials Si2Bi2. The local symmetry breaking produces opposite out-of-plane dipole moments at the top and bottom atomic sublayers leading to the R-2 spin layer locking as well as hidden orbital Rashba effects. Interestingly, we further reveal that the competition between the sublayer-sublayer interaction and the spin-orbit coupling plays a crucial role in determining the R-2 spin layer locking. |
Wednesday, March 17, 2021 9:12AM - 9:24AM Live |
L36.00007: Non-orthogonal spin-momentum locking in strongly spin-orbit coupled materials Wei-Chi Chiu, Tugrul Hakioglu, Robert Markiewicz, Bahadur Singh, Arun Bansil Orthogonal spin-momentum locking is a general feature of the Rashba spin-orbit coupled surfaces. Recently, experimental evidence for non-orthogonal spin-momentum locking (NOSML) has been reported on the topological surface of α-Sn. [1] Here, we discuss the non-magnetic impurity scattering as a candidate mechanism to this isotropic NOSML state. Our results are applicable to spin-orbit coupled systems generally and are not limited to topological states. The NOSML state is of interest in understanding and identifying spin-orbit dependent phenomena and their spectroscopic signatures in topological and non-topological materials. |
Wednesday, March 17, 2021 9:24AM - 9:36AM Live |
L36.00008: Nonequilibrium Noise Measurement of a spin current induced by the spin Seebeck effect Xuanhan Zhao, Liyang Chen, Douglas Natelson, Changjiang Liu, Deshun Hong, Anand Bhattacharya In one implementation of the spin seebeck effect, a net angular momentum current is driven from a ferrimagnetic insulator into a nonmagnetic metal due to an applied temperature gradient. This phenomenon has shown its significance for studies of fundamental spintronic physics and potential thermoelectric applications. Nonequilibrium charge noise (or charge “shot”) noise is the inherent fluctuations in the charge current in a driven conductor due to the discreteness of charge carriers. An analogous spin shot noise is predicted to be an outstanding experimental probe for physics in spin transport in which angular momentum is carried by discrete magnons. Here we report initial results in attempting to measure the nonequilibrium spin current noise in a junction comprising a ferrimagnetic insulator Y3Fe5O12 (YIG) and the strong spin-orbit coupling paramagnetic metal Pt, with the spin current driven by the spin Seebeck effect. |
Wednesday, March 17, 2021 9:36AM - 9:48AM Live |
L36.00009: Design principles for selecting interfaces between Rashba compound and a ferroelectric film that would reverse spin texture Xiaoli Zhang, Carlos Mera Acosta, Alex Zunger The reversal of Rashba (R) dipoles and thus the ensuing spin texture is expected to be achieved at interfaces between a ferroelectric (FE) compound and a R compound upon the switching of the FE polarization. However, not all the FE/R pairs can accomplish such reversal. Using DFT calculations, a set of epitaxial interfaces between a PbTiO3 FE film and a variety of top layer materials acting as permanent or induced R films have been investigated. We find the minimal design principles leading to R spin texture reversal through ferroelectric switching. These conditions include: (i) The two FE polarizations must be retained after the interface atomic relaxation; (ii) The direction of electron transfer between the FE and R must be reversed when the FE polarization is switched; (iii) the R dipole must be reversed at least in one of its vector component directions when the FE polarization is switched; (iv)The R bands must have orbital components parallel to the direction of the reversed R dipole component. We give examples where these conditions are or are not satisfied, examining the consequences on texture, thus enabling better understanding of the microscopic features that control the desired R spin texture reversal. |
Wednesday, March 17, 2021 9:48AM - 10:00AM Live |
L36.00010: Inverse design of co-functionaity: Discovery of Rashba materials that are also topological insulators and Rashba materials that are also ferroelectrics Carlos Mera Acosta, Adalberto Fazzio, Gustavo Dalpian, Alex Zunger We demonstrate design of two types of cross fuctionalities involving co existence of the Rashba effect with “effect X”=either topology or ferroelectricity. (a) Rashba topological insulators [Matter 3, 145 (2020)]: strong Rashba effect -- as measured by the Rashba coefficient αR -- is required for various applications but the physical mechanism defining the Rashba scale, i.e., the magnitude of αR, is unknown. We predict an intrinsic separation between strong Rashba effect associated with band anti-crossing (BAC), and weak Rashba effect with no BAC. We then design 199 novel fabricated Rashba materials. Since topological insulators (TIs) intrinsically have BACs, all non-centrosymmetric TIs have large Rashba coefficient, which establishes the cross-functionality of topological Rashba insulators illustrated here for 3 cases. We find 12 such compounds. (b) Rashba Ferroelectric [Phys. Rev. B 102, 144106 (2020)]: we demonstrate the inverse design of ferroelectric Rashba materials, in which the different electric polarization directions provided by ferroelectricity have also opposite spin-polarization. These compounds thus allow the electrical reversion of spin-polarization. We find 52 ferroelectric Rashba compounds. |
Wednesday, March 17, 2021 10:00AM - 10:12AM Live |
L36.00011: Magnetic Hamiltonian Engineering by Light-Matter Interaction Zexun Lin, Martin Rodriguez-vega, Gregory Fiete In this work, we explore the flexibility and magnitude of Hamiltonian engineering by photon-phonon coupling. We consider the control of magnetism in simple toy models, and extend our results to more realistic models. |
Wednesday, March 17, 2021 10:12AM - 10:24AM On Demand |
L36.00012: Spin texture and Berry phase of heavy-mass holes confined in SiGe two-dimensional quantum well system under the coexistence of Rashba and Dresselhaus spin-orbit interactions Tatsuki Tojo, Kyozaburo Takeda We study the spin texture (ST) and Berry phase (BP) of heavy-mass holes (HHs) confined in the SiGe two-dimensional quantum well system, focusing on the coexistence of Rashba (R) and Dresselhaus (D) spin-orbit interactions (SOIs). We extend DKK's k.p perturbation approach by take into account the R- and D-relating SOIs up to the 2nd-order terms crossing with k.p term, and computationally explore ST and BP. The coexistence of both types of SOIs removes the C4 symmetry from ST, and the C2 symmetry results. The R-SOI orients spin to the tangential direction of the equi-energy surface, whereas the D-SOI causes the directional discrepancy from the contour line. |
Wednesday, March 17, 2021 10:24AM - 10:36AM Not Participating |
L36.00013: Orbital Magnetoelectric effect in px-py Zigzag nanoribbon. Tarik Cysne, Luis Canonico, Filipe Guimarães, Roberto Muniz, Tatiana G Rappoport Motivated by the recent synthetization of the monolayer of bismuthene on SiC substrate, which can be effectively described by a simple two orbitals model with strong atomic spin-orbit coupling, we study the spin and orbital angular momentum response in px-py zigzag nanoribbon to an applied longitudinal electric field. The electric field induces a finite nonequilibrium spin and orbital angular momentum along the lines of the ribbon. When only SOC is present, the sum of induced spin and orbital angular momentum over lines of the ribbon adds up to zero. When a sublattice potential induced by the substrate is included in the Hamiltonian, due to the break of spatial-inversion symmetry, the total spin on the ZZ ribbon still vanishing, but the total orbital angular momentum acquires a finite value pointing to the existence of a magnetoelectric effect in the orbital degree of freedom. Our result suggests that nanoribbons made of multi-orbital materials, such as bismuthene, can be used to found cleary signatures of non-trivial orbital-phenomena and serve as a versatile platform to the emergent field |
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