Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session R42: Spins in Semiconductors, Hyperfine and SpinOrbit CouplingFocus

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Sponsoring Units: GMAG DMP DCOMP FIAP Chair: Gian Salis, IBM Zurich Room: 389 
Thursday, March 16, 2017 8:00AM  8:12AM 
R42.00001: Characterization of spinorbit fields in InGaAs quantum wells Gian Salis, Tobias Henn, Lukas Czornomaz Narrowgap semiconductors exhibit strong spinorbit interaction and are therefore of interest for spinbased quantum devices and for Majorana zero modes. We investigate coherent electronspin dynamics and the size and symmetry of spinorbit interaction in InGaAs/InAlAs quantum wells from 10 K to room temperature using timeresolved Kerr rotation. The spin lifetime exceeds 1\,ns at 10\,K and decreases with temperature. By imprinting a diffusive velocity on the measured electron spins [1], the spinorbit energy is measured as a change in spin precession frequency. A Rashba symmetry of the spinorbit interaction is determined with a Rashba coefficient of 2$\times$10$^{12}$\,eVm [2]. This technique can be applied to other narrowgap semiconductors without the need to lithographically process the sample or to apply electrical signals.\newline [1] M.~Kohda {\em et al.}, Appl.~Phys.~Lett.~{\bf 107}, 172402 (2015).\newline [2] T. ~Henn {\em et al.}, Appl.~Phys.~Lett.~{\bf 109}, 152104 (2016).\newline [Preview Abstract] 
Thursday, March 16, 2017 8:12AM  8:24AM 
R42.00002: Currentinduced spin polarization in InGaAs and GaAs epilayers as a function of doping density Marta LuengoKovac, Simon Huang, Davide Del Gaudio, Jordan Occena, Rachel Goldman, Vanessa Sih Current induced spin polarization (CISP) is a phenomenon in which an applied electric field produces a bulk spin polarization. We performed crystalaxis dependent measurements of CISP and spinorbit (SO) splitting in seven Sidoped In$_x$Ga$_{1x}$As samples with different Indium concentrations and doping densities. In all samples, we found a negative differential relationship between the magnitude of the CISP and SO splitting. Since this is contrary to what is predicted by the RashbaEdelstein equation, which includes only intrinsic SO contributions, we conclude that extrinsic polarization mechanisms dominate. This is corroborated by temperaturedependent spin dephasing time measurements, which show that the contribution from the extrinsic ElliotYafet dephasing mechanism is comparable to or greater than the contribution from the intrinsic D’yakonovPerel’ dephasing mechanism. It is also consistent with measurements performed on GaAs, in which we measured CISP despite the samples having no measurable SO fields. We also found that samples with larger doping densities and Indium concentrations had greater CISP, consistent with our expectations. [Preview Abstract] 
Thursday, March 16, 2017 8:24AM  8:36AM 
R42.00003: Driving Pure Spin Currents With DynamicNuclearPolarization Gradients Nicholas Harmon, Michael Flatt\'e Gradients in dynamic nuclear polarization naturally develop near donor atoms in doped semiconductors, like nGaAs, that are pumped with electronic spin polarization. Recent work has demonstrated that the nuclear gradients play a role in spin dynamics and spin relaxation [1,2]. We predict a new type of spin current to occur when an external magnetic field is appropriately aligned with the gradient of a dynamically polarized nuclear field. In such cases, a linear spinsplit dispersion appears in the Landau Hamiltonian which gives rise to a spindependent velocity that separates opposite spins and produces a pure spin current. Unlike the spin Hall effect with spin Hall conductivities much less than the charge conductivity, our gradientdriven spin current utilizes the charge conductivity. We propose optical orientation experiments to demonstrate this outcome. [1] N. J. Harmon, T. A. Peterson, C. C. Geppert, S. J. Patel, C. J. Palmstrøm, P. A. Crowell, and M. E. Flatt\'e, Phys. Rev. B 92, 140201(R) (2015). [2] Y.S. Ou, Y.H. Chiu, N. J. Harmon, P. Odenthal, M. Sheffield, M. Chilcote, R. K. Kawakami, and M. E. Flatt\'e, Phys. Rev. Lett. 116, 107201 (2016). [Preview Abstract] 
Thursday, March 16, 2017 8:36AM  9:12AM 
R42.00004: Prolonging the quantum coherence of semiconductor spins Invited Speaker: Edwin Barnes Powerful future technologies based on electronic spins in semiconductors require an unprecedented level of control over the spins. One of the greatest challenges in achieving this control is the decoherence induced by the environment, a problem which is particularly severe in the context of nanoscale quantum devices. In this talk, I will present recent progress in understanding quantitatively the primary sources of decoherence for spins in semiconductor nanostructures, namely the hyperfine interaction with nuclear spins and charge fluctuations. I will present new theoretical techniques that capture the effects of multiple noise sources on the evolution of the spin coherence and show how they can be used to develop new ways to characterize and mitigate noise. I will then describe a new general theory for combatting decoherence by driving the system in such a way that decoherence effects destructively interfere and cancel out, enabling precise and robust control of a broad range of coherent quantum systems. [Preview Abstract] 
Thursday, March 16, 2017 9:12AM  9:24AM 
R42.00005: Manipulation of coherent spin dynamics using magnetic focusing in spinorbitcoupled nanostructures ShunTsung Lo, ChinHung Chen, JuChun Fan, Luke Smith, Graham Creeth, CheWei Chang, Michael Pepper, Jonathan Griffiths, Ian Farrer, Harvey Beere, Geb Jones, Dave Ritchie, TseMing Chen Spinorbit interaction is one of the key ingredients to achieving full control of coherent spin dynamics without relying on ferromagnetism. Previously, the inability to spatially separate electrons with up and down spins has limited the ability to track and use their individual spin dynamics, and hampered the versatility of a spinorbitcoupled material in both fundamental research and device design. In this work, we demonstrate that the spatial spin splitting of a coherent beam of electrons can be realized using the interplay between an external magnetic field and spinorbit interactions in semiconductor nanostructures. The technique of transverse magnetic focusing is utilized to probe the spin separation. Furthermore, our ability to tune spinorbit interactions not only makes the separation between them controllable but also enables us to individually manipulate the coherent spin dynamics of each spin species and hence their correlation. This spin focusing technique paves a way to access and manipulate two spin species simultaneously, which could be essential for spinbased quantum information processing. [Preview Abstract] 
Thursday, March 16, 2017 9:24AM  9:36AM 
R42.00006: Spin decoherence and dephasing in metal organic perovskites N. Gundlach, P. Odenthal, Y. Yao, C. Zhang, D. Sun, ZG. Yu, Z. V. Vardeny, Y. S. Li Metal organic perovskites have recently generated significant interest, particularly for photogalvanics. Experimental results have shown several characteristics of perovskite materials that make them viable for spintronic applications. Our previous research has revealed that CH$_{\mathrm{3}}$NH$_{\mathrm{3}}$PbI$_{\mathrm{3}}$ exhibits a long spin lifetime, and determined the electron and hole gfactors. Further study revealed a nonmonotonic dependence of the ensemble transverse spin lifetime T$_{\mathrm{2}}^{\mathrm{\ast }}$ on applied transverse magnetic field. While gfactor distribution leads to spin dephasing that generally decreases T$_{\mathrm{2}}^{\mathrm{\ast }}$ with increasing transverse magnetic field, the nonmonotonic dependence suggests that carrier spin dynamics are strongly affected by internal local magnetic fields. We will present our systematic study of the spin lifetimes in transvers and longitudinal magnetic fields, and discuss possible factors that contribute to spin decoherence and dephasing in the leadhalide perovskites. We acknowledge funding from the University of Utah and the Department of Energy Office of Science (DESC0014579). [Preview Abstract] 
Thursday, March 16, 2017 9:36AM  9:48AM 
R42.00007: Dissipationless transport of spinpolarized electrons and Cooper pairs in an electron waveguide J. Levy, A. Annadi, S. Lu, G. Cheng, A. TylanTyler, M. Briggeman, M. Tomczyk, M. Huang, D. Pekker, P. Irvin, H. Lee, J.W. Lee, C.B. Eom Electron systems undergo profound changes in their behavior when constrained to move along a single axis. To date, clean onedimensional (1D) electron transport has only been observed in carbonbased nanotubes and nanoribbons, and compound semiconductor nanowires. Complexoxide heterostructures can possess conductive twodimensional (2D) interfaces with much richer chemistries and properties, e.g., superconductivity, but with mobilities that appear to preclude ballistic transport in 1D. Here we show that nearly ideal 1D electron waveguides exhibiting ballistic transport of electrons and nonsuperconducting Cooper pairs can be formed at the interface between the two band insulators LaAlO$_3$ and SrTiO$_3$. The electron waveguides possess gate and magneticfield selectable spin and charge degrees of freedom, and can be tuned to the onedimensional limit of a single spinpolarized quantum channel. The strong attractive electronelectron interactions enable a new mode of dissipationless transport of electron pairs that is not superconducting. The selectable spin and subband quantum numbers of these electron waveguides may be useful for quantum simulation, quantum informatio [Preview Abstract] 
Thursday, March 16, 2017 9:48AM  10:00AM 
R42.00008: SpinOrbit Assisted ChiralTunneling at semiconductor tunnel junctions. Study with advanced 30band k. p methods. HENRI JAFFRES, THI HUONG DANG, EKATERINA ERINA, VIATCHESLAV SAFAROV, HOAI NGUYEN, HENRIJEAN DROUHIN We report on theoretical investigations and advanced k.p calculations of carrier forward scattering asymmetry vs. their incidence through interfaces and magnetic tunnel junctions (MTJ) made of semiconductors involving spinorbit interactions (SOI). This study represents an extension to our previous contribution1 dealing with the role, on the electronic forward scattering asymmetry of the Dresselhaus interaction in the conduction band (CB) of MTJs. The role of the atomicSOI of semiconductors is investigated afterwardsWe first developed a perturbative scattering method based on Green's function formalism and applied to the orbitally degenerated CB and VB to explain the calculated asymmetry. This particular asymmetry features are perfectly reproduced by advanced k. p tunneling approaches (30band) in agreement with the Green's function methods at the first perturbation order in the SOI strength. This forward scattering asymmetry leads to skewtunneling effects involving the branching of evanescent states waves. Recent experiments involving nonlinear resistance variations vs. the transverse magnetization direction or current direction in the inplane current geometry may invoke by the phenomenon we discuss. [Preview Abstract] 
Thursday, March 16, 2017 10:00AM  10:12AM 
R42.00009: Spin precession and spin waves in a chiral electron gas: beyond Larmor’s theorem Shahrzad Karimi, Florent Baboux, Florent Perez, G. Karczewski, T. Wojtowicz, Carsten Ullrich Larmor's theorem holds for magnetic systems that are invariant under spin rotation. In the presence of spinorbit coupling this invariance is lost and Larmor's theorem is broken: for systems of interacting electrons, this gives rise to a subtle interplay between the spinorbit coupling acting on individual singleparticle states and Coulomb manybody effects. We consider a quasitwodimensional, partially spinpolarized electron gas in a semiconductor quantum well in the presence of Rashba and Dresselhaus spinorbit coupling. Using a linearresponse approach based on timedependent densityfunctional theory, we calculate the dispersions of spinflip waves. We obtain analytic results for small wavevectors and up to second order in the Rashba and Dresselhaus coupling strengths $\alpha$ and $\beta$. Comparison with experimental data from inelastic light scattering allows us to extract $\alpha$ and $\beta$ as well as the spinwave stiffness very accurately. We find significant deviations from the local density approximation for spindependent electron systems. [Preview Abstract] 
Thursday, March 16, 2017 10:12AM  10:24AM 
R42.00010: Dispersive chiralspin modes in a 2D FermiLiquid with spinorbit coupling. Dmitrii Maslov, Saurabh Maiti Chiralspin modes in a 2D Fermi liquid with spinorbit coupling are oscillations of magnetization in zero magnetic field resulting from a manybody effect. We study the qdispersion of these modes in the presence of both Rashba and Dresselahaus spinorbit coupling and inplane magnetic field. We show, both by symmetry arguments and explicit calculations, that the dispersion contains a leading linear in q term, which is a unique feature of spinorbit coupling. The massive (q=0) part of the mode varies with direction of the inplane magnetic field. These features have been observed in a series of Raman experiments in CdMnTe quantum well but were interpreted as an indication of a strong renormalization of spinorbit coupling by electronelectron interaction. We show that the data can be explained without invoking strong renormalization effects. We also predict that these modes should be observed even in the absence of the magnetic field. [Preview Abstract] 
(Author Not Attending)

R42.00011: Spininterference in complex spinorbit fields in ring systems Henri Saarikoski, Fumiya Nagasawa, M. Wang, Junsaku Nitta We consider here interplay between complex spinorbit (SO) and magnetic fields in spininterference experiments in mesoscopic semiconductor ring systems. We specifically focus on Dresselhaus[001] spinorbit interaction and Rashba spinorbit interaction, as well as an inplane magnetic field. In a twodimensional (2D) electron gas subject to these SO fields weak localization effects has been predicted to give rise to anisotropic magnetoresistance as a function of inplane field direction [A. G. Mal'shukov et al., Phys. Rev. B 59, 5702 (1999)]. However, experimental data in mesoscopic ring arrays indicates surprisingly that there is a phase shift in anisotropy as a function of spinorbit field which is in contrast to the calculations for the 2D electron gas. We show both 1D and 2D theoretical calculations and propose that this is due to spin interference effects in the ring geometry and anisotropy from the wire is weak. We demonstrate significant 2D effects arising in multimode wires. [Preview Abstract] 
Thursday, March 16, 2017 10:36AM  10:48AM 
R42.00012: Multiorbital induced effective Rashba spin texture  the inequivalent contribution MingChien Hsu, LiangZi Yao, Seng Ghee Tan, Mansoor B. A. Jalil, Gengchiau Liang Many important methods controlling spin in solids have been realized by Rashba effect inheriting from the interaction between spin and orbitals. However, it is usually discussed on the spin part only, while there may be increasing need to understand the role of orbitals in fields like orbitronics and spin orbit torque. Recently it was demonstrated that the orbital angular momentum texture is the basis resulting in Rashba spin texture. To better understand how various quantities influence the spin texture, the effective Rashba splitting in multiorbital systems is reinvestigated. For systems with p orbitals, two pairs of Rashba splitting with opposite signs emerge and the last one remains near degenerate, consistent with previous works. However, it is found that the amplitudes of two pairs of Rashba texture differ, not as claimed to be equal previously. This explains why usually only one significant spin splitting was observed, obscuring the discovery of orbital contributions. Both the analytical derivation and ab initio simulation show consistent results. Physical parameters like the spinorbit coupling strength, the inversion asymmetry, and the crystal field are tuned to see how all pairs of spin texture change, demonstrating ways to control them more diversely in the future. [Preview Abstract] 
Thursday, March 16, 2017 10:48AM  11:00AM 
R42.00013: Universality of lowenergy Rashba scattering Joel Hutchinson, Joseph Maciejko In twodimensional (2D) crystals with broken inversion symmetry, the spin degeneracy of the electronic band structure may be lifted by Rashba spinorbit coupling. The resulting spinsplit dispersion is responsible for the spin Hall effect and can also be observed in ultracold atoms. This spinsplit dispersion is described in terms of two distinct helicity bands, but below a threshold energy, electrons are confined to one of these. At the bottom of this lower band, the density of states is enhanced to form a van Hove singularity. This is the relevant regime for a dilute spinorbit coupled 2D electron gas, which has been shown to host a variety of exotic phases in the presence of electronelectron interactions. In this limit, electron scattering from a hard disk potential has been shown to exhibit an unusual onedimensional characteristic in its S matrix and scattering crosssection. In this talk we show that this behaviour is universal for Rashba scattering off of any circular, finite range potential. This is relevant both for impurity scattering in the noninteracting limit as well as for shortrange twoparticle scattering in the interacting problem. A generic solution of the T matrix is computed, which enforces the onedimensional character of the scattering physics. [Preview Abstract] 
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