Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session Y21: Spin Transport and Magnetism in 1D and 2D MaterialsFocus
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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Igor Zutic, State Univ of NY - Buffalo Room: LACC 309 |
Friday, March 9, 2018 11:15AM - 11:27AM |
Y21.00001: Out-of-plane carrier spin in transition-metal dichalcogenides under electric current Xiao Li, Hua Chen, Qian Niu Broken spatial inversion symmetry allows a nonequilibrium spin polarization to be induced by electric currents, which in two-dimensional systems is conventionally analyzed using Rashba model, leading to in-plane spin polarizations. We propose the out-of-plane carrier spin can emerge in ferromagnetic transition-metal dichalcogenides monolayer, by symmetry arguments and first-principles calculations. An intrinsic spin-orbit coupling in the monolayer provides valley-contrasting Zeeman-type spin splitting for generating the vertical induced spin. The current direction can be exploited to tune the induced spin, accompanied with valley polarization. The exotic spin accumulation paves an accessible way for perpendicular magnetization switching and electric control of valleys. |
Friday, March 9, 2018 11:27AM - 11:39AM |
Y21.00002: Electronic Transport in InSb Nanowires with Ferromagnetic Contacts Zedong Yang, Sasa Gazibegovic, Diana Car, Erik P. A. M. Bakkers, Vlad Pribiag InSb nanowires have been established as a versatile materials platform for realizing Majorana bound states and for investigating spin-orbital interaction (SOI) and large effective g-factor. By coupling InSb nanowires to ferromagnetic (FM) contacts, a spin-polarized current can be injected into the nanowires and subsequently controlled by electric fields. Moreover, when only a single subband is occupied, such nanowires are expected to host a spin-helical liquid, which acts as an efficient quantum spin-filter. We will report on our progress fabricating nanowire devices with FM electrodes in spin-valve geometry, as well as discussing our low-temperature transport experiments on these devices. |
Friday, March 9, 2018 11:39AM - 11:51AM |
Y21.00003: Imaging spin diffusion in germanium at room temperature Carlo Zucchetti, Federico Bottegoni, Celine Vergnaud, Franco Ciccacci, Giovanni Isella, Lavinia Ghirardini, Michele Celebrano, Fabian Rortais, Alberto Ferrari, Alain Marty, Marco Finazzi, Matthieu Jamet The aim of spintronics is to exploit the spin degree of freedom to add new functionalities to electronic devices and boost their performances. Germanium is one of the most appealing materials for spintronic applications, thanks to its compatibility with the Si platform, the long electron spin lifetime, and the optical properties matching the conventional telecommunication window. Here, we implement a nonlocal spin injection/detection scheme in germanium at room temperature. The nonlocal geometry is particularly interesting in spintronics since it allows, in principle, spin manipulation in the channel between the spin injector and detector. By performing optical spin injection through a set of lithographically-defined metal microstrips, we demonstrate lateral spin transport in a lightly n-doped bulk Ge sample. Nonlocal spin detection is achieved using either magnetic tunnel junction or the inverse spin-Hall effect (ISHE) in a Pt stripe. With this setup, we directly map the spin diffusion in Ge, and, by combining optical spin orientation and the ISHE in Pt, we build a nonlocal spin-injection/detection scheme without the use of any ferromagnetic metal. |
Friday, March 9, 2018 11:51AM - 12:03PM |
Y21.00004: Semiconductor nanowires: Tracing spin relaxation into the one-dimensional quantum regime Florian Dirnberger, Jan König, Moritz Forsch, Christian Schüller, Tobias Korn, Dominique Bougeard Being able to control the dimensionality of semiconductor devices is a key ingredient of many quantum technology concepts. While a broad spectrum of two- or zero-dimensional semiconductor systems have been successfully established, the realization of quantum-confined one-dimensional (1D) semiconductors is much more challenging. Consequently, for example, experimental investigations of the properties of spins in 1D nanostructures have been rare. |
Friday, March 9, 2018 12:03PM - 12:15PM |
Y21.00005: Spin Wave Transport in a Graphene Quantum Hall Ferromagnet Di Wei, Toeno Van der Sar, Seung Hwan Lee, Kenji Watanabe, Takashi Taniguchi, Bertrand Halperin, Amir Yacoby We report the observation of neutral spin-excitations in a graphene quantum Hall (QH) ferromagnet. The integer quantum Hall effect is often considered to be a single-particle phenomenon in which electron-electron interactions can be ignored. However, for certain integer Landau level filling factors, these interactions cause electron spins to spontaneously polarize into a ferromagnetic state. In our experiments we focus on the ν = 1 QH ferromagnet in monolayer graphene at low temperatures and high magnetic fields. We create an imbalance in chemical potential between two edge states adjacent to the insulating ferromagnetic bulk, exceeding the minimum energy for a magnon to be generated (the Zeeman energy). This allows electrons to equilibrate to lower energies by flipping their spins, thereby launching magnons into the ferromagnet. A reverse process occurs at distant sites in the device where magnons are absorbed at a pair of oppositely spin polarized edge channels, resulting in a redistribution of chemical potential between the channels, and a change to the conductance. Using a multi-terminal device, we are able to measure a non-local signal that indicates chargeless spin transfer through the insulating bulk. |
Friday, March 9, 2018 12:15PM - 12:27PM |
Y21.00006: Tuning the conductance quantization in a high spin-orbit coupling material Michaela Trottmann, Martin Wieand, Dieter Schuh, Dominique Bougeard The control of spin-orbit fields in one-dimensional (1D) ballistic transport systems is a key element for the realization of several all-electrical concepts in the field of semiconductor spin-orbitronics. A convenient implementation of ballistic 1D transport is based on gateable two-dimensional high-mobility electron gases (2DEG). An attractive model system offering high intrinsic spin-orbit interaction is a 2DEG in InAs embedded in InAlAs/InGaAs potential walls. |
Friday, March 9, 2018 12:27PM - 12:39PM |
Y21.00007: Magnetic extension of a topological insulator surface: a novel material platform for the quantum anomalous Hall and topological magnetoelectric effects Mikhail Otrokov, Tatiana Menshchikova, Maia Vergniory, Igor Rusinov, Alexandra Vyazovskaya, Yury Koroteev, Gustav Bihlmayer, Arthur Ernst, Pedro Echenique, Andres Arnau, Evgueni Chulkov An interplay of SOC and intrinsic magnetism is known to give rise to the quantum anomalous Hall and topological magnetoelectric effects under certain conditions. Their realization could open access to low power consumption electronics as well as many fundamental phenomena. Unfortunately, being realized very recently, these effects are only accessible at extremely low temperatures and the lack of appropriate materials that would enable the temperature increase is a most severe challenge. He we present a novel material platform with unique combination of properties that is perfectly suitable for the realization of both effects at elevated temperatures. The key element of the computational material design is a magnetic extension of a topological insulator surface by a thin film of ferromagnetic insulator, which is both structurally and compositionally compatible with the topological insulator [1]. Following this proposal, we suggest a variety of specific systems and discuss their numerous advantages. |
Friday, March 9, 2018 12:39PM - 12:51PM |
Y21.00008: Bulk vs interface effects on the inverse spin-Hall effect in C70 thin films Marzieh Kavand, Jingying Wang, Hans Malissa, Zeev Vardeny, Christoph Boehme Ferromagnetic resonance induced spin pumping allows for the generation of pure spin currents by ferromagnetic materials into non-magnetic materials [1,2]. Spin pumping can be observed using spin to charge conversion as provided by the inverse Spin-Hall effect (ISHE), which, for carbon based semiconductors with generally weak SOC, is very subtle, yet detectable when pumped by very powerful ferromagnetic resonant pulses (FMR) [1]. We have studied the ISHE in fullerene C70 thin films. Repeated ISHE measurements were conducted on films with varying thickness between 10 nm and 60 nm showing that, while the ISHE current decreases with an increasing ratio of film thickness and spin diffusion length, the spin Hall angle obtained from these measurements reproduces within the error margins, suggesting that there is no thickness dependence of the mechanism behind the ISHE. This confirms our hypothesis that the measured ISHE is a bulk effect and not an interface effect. [1] D. Sun et al., Nat. Mater. 15 863-869 (2016). [2] S. Watanaba et al., Nature Phys. 10 308-313 (2014). |
Friday, March 9, 2018 12:51PM - 1:03PM |
Y21.00009: Interlayer Exchange Coupling across Graphene and h-BN junctions Debapriya Chaudhuri, Ali HALLAL, Hongxin Yang, Mair CHSHIEV Cobalt (Co)|Graphene and Co|hBN junctions are of great interest for graphene spintronics [1,2,3]. We present a comparative study of interlayer exchange coupling (IEC) between Co layers across graphene and hBN using first-principles calculations. IEC is calculated as a function of Co thickness for single graphene and hBN layer for three different FCC arrangements, namely AB, AC and BC. A RKKY type oscillatory exchange coupling constant alternating between strongly antiferromagnetic (AF) and weakly ferromagnetic (FM) is found. In FCC Co, the largest IEC is -200 meV for 5 monolayers of Co for AB type stacking whereas the HCP Co yields a coupling strength of -229 meV for AC type stacking, respectively. Finally, IEC as for hBN layer shows opposite phase for AB (12 meV) and AC/BC (-15 meV) FCC stackings. Thus, a control over the ICE gives a tunable parameter for synthetic antiferromagnetic structures in spintronics [4]. |
Friday, March 9, 2018 1:03PM - 1:15PM |
Y21.00010: Valley Edelstein effect in monolayer transition metal dichalcogenides Katsuhisa Taguchi, Tong Zhou, Yuki Kawaguchi, Yukio Tanaka, Kam Tuen Law In this work, we predict the emergence of the valley Edelstein Effect (VEE), which is an electric-field-induced spin polarization effect, in gated monolayer transition metal dichalcogenides (MTMDs). We found an unconventional valley-dependent response in which the spin-polarization is parallel to the applied electric field with opposite spin-polarization generated by opposite valleys. This is in sharp contrast to the conventional Edelstein effect in which the induced spin-polarization is perpendicular to the applied electric field. We identify the origin of VEE as combined effects of conventional Edelstein effect and valley-dependent Berry curvatures induced by coexisting Rashba and Ising SOCs in gated MTMDs. Experimental schemes to detect the VEE are also considered. |
Friday, March 9, 2018 1:15PM - 1:27PM |
Y21.00011: Skew Scattering in Graphene with Proximity Spin-Orbital Effects Manuel Offidani, Frederico Sousa, Tarik Cysne, Tatiana Rappoport, Roberto Raimondi, Aires Ferreira The generation of spin currents in nonmagnetic materials via purely electrical means has fascinated scientists since the first experimental reports of spin Hall effect (SHE) a decade ago. The SHE finds its origin in the rich charge-spin-coupled dynamics triggered by strong spin–orbit interactions. While the SHE has been detected univocally in metals and semiconductors, the design of nanostructures allowing the electrostatic control of spin Hall currents remains a big challenge. In this work, we theoretically show that skew scattering is ubiquitous in graphene-based heterostructures where mirror reflection and sublattice symmetry are simultaneously broken. Unlike conventional skew scattering-driven SHE, which requires spin–orbit-active or magnetic impurities, the skewness mechanism unveiled here results from the out-of-plane tilting of the eigenstates’ spin texture and thus it manifests for generic impurity disorder. Our results open realistic prospects for the all-electrical control of spin currents in van der Waals heterostructures of much current interest. |
Friday, March 9, 2018 1:27PM - 1:39PM |
Y21.00012: Evolution of magnetic Dirac bosons in a honeycomb lattice Daniel Boyko, Alexander Balatsky, Jason Haraldsen We examine the presence and evolution of magnetic Dirac nodes in the Heisenberg honeycomb lattice. Using linear spin theory, we evaluate the collinear phase diagram as well as the evolution of the spin dynamics with various exchange interactions. We show that the ferromagnetic structure produces bosonic Dirac and Weyl points due to the competition between super-exchange interactions. Furthermore, it is shown that the criteria for magnetic Dirac nodes are coupled to magnetic structure and not the overall crystal symmetry, where the breaking of inversion symmetry greatly affects the antiferromagnetic configurations. The tunability of the nodal points through variation of the exchange parameters leads to the possibility of controlling Dirac symmetries through external manipulation of the orbital interactions. |
Friday, March 9, 2018 1:39PM - 1:51PM |
Y21.00013: Bose-Einstein condensation of Dirac magnons Saikat Banerjee, Alexander Balatsky The discovery of graphene, a two dimensional material which hosts massless linearly dispersive quasiparticles, has led to an extensive research in Dirac fermions in the last decade. The effect of interaction in the stability and renormalization of Dirac cone attracted considerable attention. With the expanding list of fermionic Dirac materials, the idea of bosonic Dirac materials has emerged. In our previous works, we have established the notion of Dirac bosons. In this paper, we analyze and predict the condition for the formation of Bose-Einstein condensation (BEC) by Dirac magnons in Chromium tri-halides CrX3 (X= Fl, Br and I). The BEC order parameter has a spinor structure and modulates with finite momentum at the Dirac point. We also discuss the dynamics of the two component/spinorial BEC order parameter by a Dirac Gross-Pitaevskii equation. Our work is motivated by a recent experimental observation (PRL 112, 116402 (2014)) of polaritonic Bose-Einstein condensation in honeycomb lattice. |
Friday, March 9, 2018 1:51PM - 2:03PM |
Y21.00014: Anisotropic Spin-Superfluid Magnet as a Long Josephson Junction Daniel Hill, Se Kwon Kim, Yaroslav Tserkovnyak I will discuss spin transport in an insulating anisotropic ferromagnet and the insights that can be gained by mapping it onto the well studied long Josephson junction. This correspondence sheds light on the nonequilibrium phase diagram of a ferromagnetic strip subjected to spin injection at its ends. The mapping, under which magnetic-vortex solutions of a long Josephson junction correspond to domain-wall states in the ferromagnet, holds for stationary states up to a critical bias determined by the Landau criterion. In carrying over dynamic solutions, the ferromagnet requires additional considerations at the boundaries due to spin pumping. The Josephson junction analogy inspires spintronic applications based on magnetic insulators. |
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