Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C39: Spinorbit Coupling in SemiconductorsFocus

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Sponsoring Units: GMAG DCMP DMP Chair: Vlad Pribiag, University of Minnesota Room: BCEC 207 
Monday, March 4, 2019 2:30PM  3:06PM 
C39.00001: Asymmetric g Tensor in LowSymmetry TwoDimensional Hole Systems Invited Speaker: Roland Winkler Zeeman coupling characterized by the g factor is a key ingredient to developing novel spinbased technologies such as quantum information protocols. In lowsymmetry systems, the g factor becomes a secondrank tensor (a 3×3 matrix) that couples the spin to the magnetic field B. It has long been believed that this tensor g only affects the energy splitting in a magnetic field. We demonstrate [1] that it also encodes the direction of the axis about which the spins precess in the external field B. In general, this axis is not aligned with B. Using timeresolved Kerr rotation measurements performed on a sequence of lowsymmetry twodimensional hole systems in GaAs/AlAs quantum wells, we show that this feature of the tensor g manifest itself in unusual precessional motion as well as distinct dependencies of hole spin dynamics on the direction of the magnetic field B. A detailed theoretical analysis of these experiments allows us, for the first time, to determine the individual components of the full tensor g for [113], [111] and [110]grown samples. We also derive transparent analytical expressions for the components of the tensor g, complemented with accurate numerical calculations yielding very good agreement between experiment and theory. 
Monday, March 4, 2019 3:06PM  3:18PM 
C39.00002: Enhancement of the SpinOrbit Coupling in Silicon by Bismuth Doping Fabien Rortais, SOOBEOM LEE, Ryo Ohshima, Sergey Dushenko, Yuichiro Ando, Masashi Shiraishi Si possesses a low spinorbit coupling, it allows a long spin lifetime but limits new devicedesigning possibilities in spintronics, particularly with the spincharge conversion effects to create an allSi spin devices. The purpose of this study is to create a sizable spinorbit interaction in Si by implantation of a heavy element, bismuth (Bi). 
Monday, March 4, 2019 3:18PM  3:30PM 
C39.00003: Strain engineering of RashbaDresselhaus spinorbit coupling and intrinsic spinHall effect in Si Paul C Lou, Anand Katailiha, Ravindra G Bhardwaj, Sandeep Kumar The weak intrinsic spinorbit coupling and centosymmetric crystal structure are critical bottleneck in development of Si spintronics because it leads to insignificant spinHall effect (spin current generation) and inverse spinHall effect (spin current detection) even though it results into long spin diffusion length at room temperature. In this experimental study, we use strain gradient to break the structural inversion symmetry, which causes flexoelectric effect and charge separation. This leads to the RashbaDresselhaus spin orbit coupling in the bulk of Si along with Si interface. The cubic RashbaDresselhaus spinorbit coupling lifts the spin degeneracy of band structure introducing intrinsic spinHall effect, which is uncovered using spinHall magnetoresistance measurement in Ni_{80}Fe_{20}/MgO/pSi freestanding thin film. The strain gradient effects are uncovered using piezoresistive behavior due to thermal expansion induced compressive stresses. The intrinsic spinHall effect is observed in both ndoped and pdoped Si thin films. This experimental study brings the Si spintronics closer to reality. This work demonstrates that strain gradient can be used for spin current generation, detection and control in Si. 

C39.00004: ABSTRACT WITHDRAWN

Monday, March 4, 2019 3:42PM  3:54PM 
C39.00005: Unidirectional magnetoresistance in a bulk Rashba ferromagnet Ryutaro Yoshimi, Kenji Yasuda, Atsushi Tsukazaki, Minoru Kawamura, Kei Takahashi, Masashi Kawasaki, Yoshinori Tokura The Rashba effect is the spin band splitting due to broken inversion symmetry through spinorbit coupling, typically observed at surfaces and interfaces. Recently, some noncentrosymmetryic crystals have been found to have the bulk Rashba bands that are larger than surface/interface ones. Nonreciprocal transport of quantum particles such as electron, spin and phonon is known to occur by further breaking time reversal symmetry in such a material without inversion symmetry. In particular, the interplay with magnetism in spinpolarized bands may enhance the nonreciprocal charge transport. In this study, we investigated the unidirectional magnetoresistance in thin films of Ge_{1x}Mn_{x}Te, which is a bulk ferromagnetic Rashba semiconductor. The magnitude of nonreciprocal transport shows a strong dependence on carrier density, which suggests that the scattering process on Fermi surface is essential for the nonreciprocal transport in the system. 
Monday, March 4, 2019 3:54PM  4:06PM 
C39.00006: The temperature and doping dependence of inverse spin Hall effect in nGaAs Zhen Jiang, Sahil Patel, Paul Crowell, Chris Palmstrom We have carried out measurements of the inverse spin Hall effect (ISHE) in a series of nGaAs epilayers doped near the metalinsulator transition. Spin currents are generated using epitaxial Fe/GaAs (001) Schottky tunnel barriers. The ISHE is detected in a simple Hall cross geometry, and precession in a static magnetic field (the Hanle effect) is used to separate the effect from background contributions. We find that the ISHE voltage at low temperatures is much larger than expected based on previous measurements of the direct spin Hall effect. The enhancement is accompanied by significant distortion of the Hanle curves, suggesting that hyperfine interactions play a significant role. Comparison with nonlocal spin valve measurements over the entire doping range (3 x 10^16 cm^3 to 7 x 10^16 cm^3) and at temperatures up to 110 K indicates that local inhomogeneities in the hyperfine field, which disappear as the temperature increases, may be responsible for the enhancement. 
Monday, March 4, 2019 4:06PM  4:18PM 
C39.00007: Time resolved spectroscopy of ntype InAsP films Rathsara R Herath Mudiyanselage, Brenden A Magill, Giti Khodaparast, Joseph A Spencer, Kiara McMillan, Sukgeun Choi, Chris Palmstrom In this study, we employed ultrafast Time Resolved Differential Reflectivity (TRDR) and ultrafast time resolved Magnetooptic Kerr Effect (MOKE) on InAs_{x}P_{1x} ternary alloy. In recent years, InAs_{x}P_{1x} ternary alloys have attracted extensive attention due to the immense prospect for various optoelectronic applications including optical telecommunication, broadband photodetectors, midIR lasers, and also quantum communication devices. ^{1,2} As the switching rates in devices are pushed to higher frequencies in optoelectronic and spintronic devices, it is required to perform comprehensive studies of the carrier and spin relaxation dynamics in semiconductors on a femtosecond timescale. Here we report carrier and spin dynamics of ntype InAs_{x}P_{1x} films in a broad optical region (700 nm and 1000 nm). Also, we observed the generation of coherent oscillations which could be related to photoinduced coherent acoustic phonons. The InAs_{x}P_{1x} films are ~1.2 micron thick grown on semiinsulating InP (001) wafers and the carrier concentrations are estimated to be 1x10^{17} cm^{3}. 
Monday, March 4, 2019 4:18PM  4:30PM 
C39.00008: Protected Hidden Spin Polarization by Crystalline Symmetry in Centrosymmetric Nonmagnetic Systems Yingjie Zhang, Qihang Liu We derive a tightbinding model with spinorbital interaction to describe the band edge behaviors of a twodimensional centrosymmetric system with nonsymmorphic symmertry. The two sublattices in this structure are staggered along the normal direction, and connect each other by glide reflection operations, which plays an essential role in protecting the local Rashba spin polarization for each sublattice. By model simulation and symmetry analyses, we find that each sublattice hosts a Rashbatype spin polarization due to the local dipole field. Taking the sublattice interaction into account, The spin texture of the two sublattices around the corner of Brillouin zone still present remarkable Rashbatype vortex with exactly opposite patterns to each other, while at the Gamma point the interaction between two sublattices tends to cancel the local spin polarization. Our finding provides a promising avenue to search material candidates with strong hidden spin polarization, and thus broadens the type of materials that can be used for novel spintronic applications. 
Monday, March 4, 2019 4:30PM  4:42PM 
C39.00009: Uncovering and tailoring hidden Rashba spinorbit coupling in centrosymmetric crystals Linding Yuan, Qihang Liu, Xiuwen Zhang, JunWei Luo, ShuShen Li, Alex Zunger Hidden Rashba and Dresselhaus spinsplittings in centrosymmetric crystals having subunits (sectors) with noncentrosymmetric symmetries (the R2 and D2 effects) have been predicted and observed experimentally, but the microscopic mechanism remains unclear. Here we demonstrate that the spinsplitting in R2 is enforced by the nonsymmorphic symmetry of the wavevectors, which ensures that the pertinent spin wavefunctions segregate spatially on just one of the two inversionpartner sectors and thus avoid compensation. This finding establishes a common fundamental source for the conventional noncentrosymmetric Rashba (R1) effect and the R2 effect, both originating from the local sector symmetries, rather than from the global crystal symmetry per se. We further show that the effective Hamiltonian for the R1 effect is also applicable for the R2 effect, but applying a symmetrybreaking electric field to an R2 compound produces different spinsplitting pattern than applying a field to a trivial (nonR2) centrosymmetric compound. 
Monday, March 4, 2019 4:42PM  4:54PM 
C39.00010: Ubiquitous SpinOrbit Coupling in a Screw Dislocation with High Spin Coherency Lin Hu, Huaqing Huang, Zhengfei Wang, Wei Jiang, Xiaojuan Ni, Yinong Zhou, V Zielasek, Max G Lagally, Bing Huang, Feng Liu We theoretically demonstrate that screw dislocation (SD), a 1D topological defect widely present in semiconductors, exhibits ubiquitously a new form of spinorbit coupling (SOC) effect. Differing from the widely known conventional 2D RashbaDresselhaus (RD) SOC effect that typically exists at surfaces or interfaces, the deeplevel nature of SDSOC states in semiconductors readily makes it an ideal SOC. Remarkably, the spin texture of 1D SDSOC, pertaining to the inherent symmetry of SD, exhibits a significantly higher degree of spin coherency than the 2D RDSOC. Moreover, the 1D SDSOC can be tuned by ionicity in compound semiconductors to ideally suppress spin relaxation, as demonstrated by comparative firstprinciples calculations of SDs in Si/Ge, GaAs, and SiC. Our findings therefore open a new door to manipulating spin transport in semiconductors by taking advantage of an otherwise detrimental topological defect. 
Monday, March 4, 2019 4:54PM  5:06PM 
C39.00011: Ubiquitous Spinorbit Coupling in a Screw Dislocation of Semiconductors Bing Huang, Lin Hu, Feng Liu We demonstrate that screw dislocation (SD), a 1D topological defect widely present in semiconductors, exhibits ubiquitously a new form of spinorbit coupling (SOC) effect. Differing from the widely known conventional 2D RashbaDresselhaus (RD) SOC effect that typically exists at surfaces/interfaces, the deeplevel nature of SDSOC states in semiconductors readily makes it an ideal SOC. Remarkably, the spin texture of 1D SDSOC, pertaining to the inherent symmetry of SD, exhibits a significantly higher degree of spin coherency than the 2D RDSOC. Moreover, the 1D SDSOC can be tuned by ionicity in compound semiconductors to ideally suppress spin relaxation, as demonstrated by comparative firstprinciples calculations of SDs in Si/Ge, GaAs, and SiC. 
Monday, March 4, 2019 5:06PM  5:18PM 
C39.00012: Extreme asymmetry of 90degree domain walls in multilayered films of (Ga,Mn)(As,P) Vitalii VlaskoVlasov, WaiKwong Kwok, Sining Dong, Xinyu Liu, Malgorzata Dobrowolska, J K Furdyna We image the magnetic domain structure during remagnetization of MBE grown multilayered films of a diluted magnetic semiconductor (Ga,Mn)(As,P) with digital modulations of the phosphorus concentration. The samples show two inplane easy magnetization axes corresponding to the <100> cubic and [110] uniaxial anisotropies, typical for the GaMnAs system. Their remagnetization occurs in two steps through the nucleation and growth of 90degree domains. Unexpectedly, the domain boundaries align precisely with the easy axes in contrast to our micromagnetic calculations using the measured magnetic parameters of the samples. We discuss how such totally asymmetric Neel domain walls can appear due to DzyaloshinskiiMoriya interactions enhanced by the multiple sharp interfaces in the multilayered films. 
Monday, March 4, 2019 5:18PM  5:30PM 
C39.00013: Large perpendicular magnetic anisotropy and anisotropic electronic structure of the new ferromagnetic semiconductor (Ba,K)(Zn,Mn)_{2}As_{2} single crystal studied by angledependent xray magnetic circular dichroism Shoya Sakamoto, Guoqiang Zhao, Goro Shibata, Zheng Deng, Kan Zhao, Bijuan Chen, Yosuke Nonaka, Keisuke Ikeda, Zhendong Chi, Yuxuan Wan, Masahiro Suzuki, Tsuneharu Koide, Sadamichi Maekawa, Yasutomo J Uemura, Changqing Jin, Atsushi Fujimori (Ba_{,}K)(Zn,Mn)_{2}As_{2} is a new ferromagnetic semiconductor isostructural to 122type Febased superconductors. The Curie temperature (T_{C}) reaches 230 K for polycrystalline samples exceeding the highest T_{C} = 200 K of (Ga,Mn)As. In relation to the anisotropic crystal structure, this material has large perpendicular magnetic anisotropy. 
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