Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session S21: SpinOrbit Coupling and Spin Coherence in Semiconductor HeterostructuresFocus

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Sponsoring Units: GMAG DMP FIAP DCOMP Chair: Giovanni Vignale, Univ of Missouri  Columbia Room: LACC 309 
Thursday, March 8, 2018 11:15AM  11:27AM 
S21.00001: Unusual InPlane Field Dependence of Spin Resolved Magnetic Focussing in 2D Hole Systems Matthew Rendell, Scott Liles, Oleh Klochan, Ashwin Srinivasan, Ian Farrer, David Ritchie, Alex Hamilton The need for an allelectrical method of spin control has driven great interest in the spinorbit interaction. Transverse magnetic focussing provides a method to study spin dynamics by creating spatial separation of spin. We perform magnetic focussing of holes in high symmetry (100) GaAs/AlGaAs heterostructures. We compare focussing in single heterojunction (very strong Rashba) and quantum well (weaker Rashba) structures. While the period of the focussing peaks is the same, we discuss several features that differentiate the spin resolved peaks in these systems. By varying the focussing length we extract the focussing decay length for each spin peak. We also study the dependence of the spin peak separation on the 2D density. Finally, we observe unusual behaviour of the height of the spin peaks with inplane magnetic fields. 
Thursday, March 8, 2018 11:27AM  11:39AM 
S21.00002: Spin dynamics in manyelectron quantum dots of tunable size Sergej Markmann, Christian Reichl, Werner Wegscheider, Gian Salis The electron spin coherence time in GaAsbased quantum dots is limited by hyperfine interaction with statistical fluctuations of the nuclear spin polarization. For larger dots in the transition to a 2D system, spinorbit interaction becomes the dominant dephasing mechanism. In the region in between, a minimum dephasing is expected. Here we investigate the spin coherence time in quantum dots of tunable size obtained from dry etching of a 2D electron gas (2DEG) confined in a GaAs quantum well. Using the pumpprobe magnetooptical Kerr rotation technique, electron spin dynamics in ensembles of uniform dots is measured. The spin coherence time increases by two orders of magnitude, from 200 ps in the 2DEG, to more than 20 ns for dots with a diameter of 400 nm. A periodic optical orientation of electron spin polarization at a rate of 80 MHz induces a modelocking of the spin precession that is enhanced by orientation of nuclear spin polarization, similar to what has been observed for singly charged selfassembled quantum dots but here realized in large manyelectron quantum dots with tunable spinorbit interaction. 
Thursday, March 8, 2018 11:39AM  11:51AM 
S21.00003: Weak localization magnetoconductivity in quantum wells with Rashba and Dresselhaus spinorbit interaction  An analytic solution Domnita Marinescu, Pirmin Weigele, Carlos Egues, Dominik Zumbuhl We formulate an analytic solution to the problem of the weak localization (WL) corrections to the conductivity in the presence of a quantizing magnetic field that incorporates all three spinorbit terms that are relevant to semiconductors: linear Rashba, linear and cubic Dresselhaus. Our theory produces a complete phenomenological description of the WL contributions that showcases in a direct way the interplay between the Landau level quantization of the electron states and the spinorbitdriven spinflip processes. The form of the solution is determined by the relative strengths of the linear couplings, α for Rashba and β for Dresselhaus. Although present throughout the calculation, the cubic Dresselhaus term becomes important only in the α ≈ β case when it acts as a spinsymmetry breaking factor. All the contributions to magnetoconductivity associated with the quantification of the electron orbits are calculated in a Landau level invariant form. The analytic expression obtained for β >> α (or α >> β) becomes an exact solution when α = 0 (or β = 0). A closedform formula describes the α ≈ β regime, where the result depends only on the difference between the linear Rashba and Dresselhaus terms and the cubic Dresselhaus parameter. 
Thursday, March 8, 2018 11:51AM  12:27PM 
S21.00004: Stretching and Breaking the Persistent Spin Helix Invited Speaker: Dominik Zumbuhl We introduce the concept of the stretchable persistent spin helix (PSH), i.e. a PSH with gateadjustable pitch [1]. This opens the door for electrical spin manipulation while spins are protected from the usual DyakonovPerel spin decay when propagating through the material. To implement this, a top and back gate is employed to independently tune both the Rashba coefficient α and the effective Dresselhaus coefficient β insitu. Tunability of β was predicted ca 1990 based a density dependence in the projected 2D term. Here, we demonstrate this in an experiment [1], and we employ the suppression of weak antilocalization as a sensitive detector for matched SO fields. Varying both α and β controllably and continuously with gate voltages, we can demonstrate robust continuous locking at α=β over a wide range, thus stretching the PSH. When combined with numerics, this yields th spinorbit parameters of the system. Stretchable PSHs could provide the platform for longdistance communication ∼8–25 μm between solidstate spin qubits. 
Thursday, March 8, 2018 12:27PM  12:39PM 
S21.00005: Spinorbit coupling effects in nonlinear optical response Benjamin M. Fregoso We investigate the effects of the spinobit (SO) coupling in the shift current response of solids within the independentparticle approximation. The SO coupling introduces new terms which depend on Berry connections and strongly modify the optical response to circular polarization. Applications twodimensional ferroelectrics and singlelayer Transitions Metal Dichalcogenides are discussed. 
Thursday, March 8, 2018 12:39PM  12:51PM 
S21.00006: Surface Berry plasmons in magnetic semiconductors Giovanni Vignale, Shulei Zhang The concept of ``surface Berry plasmons" is studied in the concrete instance of a magnetic semiconductor in which the Berry curvature, generated by atomic spinorbit interaction, has opposite signs for carriers spin parallel or antiparallel to the magnetization. By using collisionless hydrodynamic equations with appropriate boundary conditions, we study both the surface plasmons of a threedimensional magnetic semiconductor and the edge plasmons of a twodimensional one. In the 3D case we calculate the dependence of the plasmon frequency on the angle between the direction of propagation and the bulk magnetization. In the 2D case we find that the frequency of the plasmon depends on the direction of propagation along the edge. These Berry curvature effects are compared and contrasted with the anisotropies induced in the plasmon dispersion by an external magnetic field in the absence of Berry curvature. We argue that Berry curvature effects may be used to control the direction of propagation of the surface plasmons, and create a link between plasmonics and spintronics. 
Thursday, March 8, 2018 12:51PM  1:03PM 
S21.00007: Optical Response in Semiconductor Quantum Wells in proximity to Chiral pwave Supercon
ductor MingWei Wu, Fei Yang By using gaugeinvariant optical Bloch equation, we investigate the optical response to 
Thursday, March 8, 2018 1:03PM  1:15PM 
S21.00008: Coupled Orbital and Spin Dynamics of Particles with Magnetic Moments Roland Winkler, E. A. Fajardo, Ulrich Zuelicke 
Thursday, March 8, 2018 1:15PM  1:27PM 
S21.00009: Abstract Withdrawn In our recent paper [1] we have studied the edge spin accumulation due to an electric current in a high mobility twodimensional electron gas formed in a symmetric well with two subbands. We have explained the results of recent experiments [2] which demonstrated the spin accumulation near the edges of a symmetric bilayer GaAs structure in contrast to no effect in a singlelayer configuration. The intrinsic mechanism of the spinorbit interaction we consider arises from the coupling between two subband states of opposite parities [3]. We showed that presence of a gap in the system (i.e., the energy separation between the two subband bottoms) changes drastically the picture of the edge spin accumulation. By increasing the gap from zero up to 1 2 K only, the magnitude of the effect changes by three orders of magnitude. We calculate the edge spin density in the presence of inplane magnetic field. We obtained strong effect of Zeeman field on the magnitude of the edge spin density since the effective gap is changed. 
Thursday, March 8, 2018 1:27PM  1:39PM 
S21.00010: Quantum transport theory: numerics and dynamics Timothy Lovorn, Akihiko Sekine, Allan MacDonald In recent years a number of systems have been identified in which momentumspace Berry phases play an important role in determining transport coefficients. Examples include the anomalous and spin Hall effects in spintronics and the negative magnetoresistance of Weyl semimetals. A convenient quantum kinetic formalism has recently been developed which is intended to allow these transport effects to be evaluated in real materials. As discussed in Refs. [1, 2], the formalism treats linear response to static electric field and nonlinear response to static magnetic field in the lowfield regime. We present a numerical implementation of this formalism, validated by comparing with analytic results for simple models but applicable to general tightbinding models. We also discuss the extension of this formalism to consider nonlinear response to a timevarying electric field, with potential application to the valley Hall effect. 
Thursday, March 8, 2018 1:39PM  1:51PM 
S21.00011: Strong Influence of Spinorbit Coupling on Magnetotransport in Twodimensional Hole Systems Hong Liu, Elizabeth Marcellina, Dimitrie Culcer, Alex Hamilton Lowdimensional hole systems have attracted considerable recent attention in the context of nanoelectronics and quantum information. They exhibit strong spinorbit coupling but a weak hyperfine interaction, which allows fast, lowpower electrical spin manipulation and potentially increased coherence times while their effective spin3/2 is responsible for physics inaccessible in electron systems. However, experimentally measuring, identifying, and quantifying spinorbit coupling effects in transport, such as electricallyinduced spin polarizations and spin Hall currents, are challenging. We show that the magnetotransport properties of twodimensional hole systems display strong signatures of the spinorbit interaction. Specifically, the lowmagnetic field Hall coefficient and longitudinal conductivity contain a contribution that is second order in the spinorbit interaction coefficient and is nonlinear in the carrier number density. We propose an experimental setup to probe these spinorbit dependent magnetotransport properties, which will permit one to extract the spinorbit coefficient directly from the magnetotransport. 
Thursday, March 8, 2018 1:51PM  2:03PM 
S21.00012: Spin Hall Effect in Ferroelectric Rashba Semiconductors Haihang Wang, Jagoda Slawinska, Silvia Picozzi, Marco Buongiorno Nardelli The coupling of different functionalities in materials has been playing an increasingly significant role in the design and discovery of devices with novel properties. In this work, we study the Spin Hall Effect (SHE) in FerroElectric Rashba SemiConductors(FERSC) in order to explore the possibility of controlling spin transport via an electric field. This study is motivated by the discovery of the spinelectric coupling effect in FERSC (eg. GeTe) which allows the switch and control of the spin texture via an electric field, and the fact that band splitting together with electric filed could eventually lead to a universal spin hall conductivity. A detailed theoretical investigation of systems such as GeTe, SnTe, and some hexagonal ABC semiconductors (eg. LiBeSb, NaZnSb) will be presented. These results are obtained using the recently developed PAOFLOW package (http://www.aflowlib.org/src/paoflow/) integrated in AFLOWπ highthroughput framework (http://www.aflowlib.org/src/aflowpi/). 
Thursday, March 8, 2018 2:03PM  2:15PM 
S21.00013: Anomalous Hall effect in epitaxial spinel NiCo_{2}O_{4} films Xuegang Chen, Xiaozhe Zhang, Xiaoshan Xu, Xia Hong We report the magnetotransport studies of the spinel ferrimagnetic NiCo_{2}O_{4} (NCO) thin films. NCO has an inverse spinel structure with the Neel temperature T_{N} above room temperature. We deposited epitaxial NCO films as thin as 2 u.c. (~1.6 nm) on (001) MgAl_{2}O_{4} substrates using offaxis magnetron sputtering, with high crystallinity and atomically smooth surface achieved. The NCO films possess an outofplane magnetic easy axis. A robust anomalous Hall effect (AHE) has been observed at the temperature range from 2 K to T_{N} of 330 K, which changes sign at ~190 K. We discuss the possible mechanisms that determine the AHE signal in the NCO films. Our study reveals the complex energy landscape in NCO due to the competition of the crystalline field with the charge and spin degrees of freedom. 
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