Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session N18: Focus Session: Spin-Dependent Phenomena in Semiconductors - Spin Orbit and Mesoscopic |
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Jean Heremans, Virginia Polytechnic Institute and State University Room: 320 |
Wednesday, March 20, 2013 11:15AM - 11:27AM |
N18.00001: Gate-control of spin polarization waves Luyi Yang, J.D. Koralek, J. Orenstein, D.R. Tibbetts, J.L. Reno, M.P. Lilly We report on control of the persistent spin helix (PSH) in semiconductor quantum wells with tunable spin-orbit (SO) coupling via external gates. The PSH is a collective spin excitation of two-dimensional electron systems that emerges as a new conserved quantity of the SU(2) symmetry. It occurs when the strengths of Rashba and linear Dresselhaus SO coupling are equal. Previously, this effect was demonstrated by a set of samples with different doping asymmetry and well width [1]. Now we fabricate samples with both front and back gates aiming to control Rashba SO coupling continuously and increase the lifetime-enhancement by reducing the symmetry-breaking cubic Dresselhaus term. \\[4pt] [1] J. D. Koralek et al., Emergency of the persistent spin helix in semiconductor quantum wells, Nature 458, 610-613 (2009). [Preview Abstract] |
Wednesday, March 20, 2013 11:27AM - 11:39AM |
N18.00002: Chiral Spin Waves in Fermi Liquids with Spin-Orbit Coupling Ali Ashrafi, Dmitrii Maslov We predict the existence of chiral spin waves--collective modes in a two-dimensional Fermi liquid with the Rashba or Dresselhaus spin-orbit coupling. Starting from the phenomenological Landau theory, we show that the long-wavelength dynamics of magnetization is governed by the Klein-Gordon equations. The standing-wave solutions of these equations describe \lq\lq particles\rq\rq\/ with effective masses, whose magnitudes and {\em signs} depend on the strength of the electron-electron interaction. The spectrum of the spin-chiral modes for arbitrary wavelengths is determined from the Dyson equation for the interaction vertex. We propose to observe spin-chiral modes via microwave absorption of standing waves confined by an in-plane profile of the spin-orbit splitting. [Preview Abstract] |
Wednesday, March 20, 2013 11:39AM - 11:51AM |
N18.00003: Magnetic control of spin-orbit fields: a first principles study of Fe/GaAs junctions Jaroslav Fabian, Martin Gmitra, Alex Matos-Abiague, Claudia Draxl The possibility to control the spin-orbit fields in semiconductor heterostructures by electric fields has been used to influence the spin dynamics of itinerant electrons. We show that the spin-orbit fields can also be controlled by magnetic fields. On the example of Fe/GaAs junctions we illustrate how the electronic band structure of ferromagnet/semiconductor interfaces, here calculated from first principles for a slab geometry using the FLEUR code, can be mapped to effective spin-orbit field Hamiltonians whose parameters are extracted directly from the band structure, without requiring a priori knowledge of the functional form of the spin-orbit fields, as has been the standard up to now. We show that the spin patterns resulting from the spin-orbit fields change qualitatively as the magnetization orientation of the junction changes in the plane of the interface. The magnetic control of spin-orbit fields is important for transport and optical magnetoanisotropies of ferromagnet/non-magnetic conductor junctions. [Preview Abstract] |
Wednesday, March 20, 2013 11:51AM - 12:27PM |
N18.00004: Stern-Gerlach effect and spin separation in InGaAs nanstructures Invited Speaker: Makoto Kohda The demonstration of quantized spin splitting by Stern and Gerlach in 1922 is one of the most important experiments in modern physics. We utilized an effective non-uniform magnetic field which originates from Rashba spin orbit interaction (SOI) and demonstrated an experimental manifestation of electronic Stern-Gerlach spin separation in InGaAs based quantum point contacts (QPCs) [1]. Lateral potential confinement in a trench-type QPC creates a spatial modulation of Rashba SOI inducing a spin dependent force Clear conductance plateaus are observed in steps of 2$e^{\mathrm{2}}$/$h $when the strength of Rashba SOI becomes small. However, when the Rashba SOI is enhanced by applying the top gate, a half-integer plateau additionally appears at 0.5(2$e^{2}/h)$, indicating the spin polarized current. We found that the spin polarization of the conduction electrons in this plateau is as high as 70{\%}. Our new approach for generating spin polarization in semiconductor nanostructures provides a way to seamlessly integrate electrical spin generation, manipulation, and detection in a single semiconductor device without the need for either external magnetic fields or magnetic materials. \\[4pt] [1] M. Kohda \textit{et al}. Nature Communications 3, 1082 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 12:27PM - 12:39PM |
N18.00005: Spin blocking effect in symmetric double quantum well due to Rashba spin-orbit coupling Satofumi Souma, Matsuto Ogawa, Yoshiaki Sekine, Atsushi Sawada, Takaaki Koga We report a theoretical study of the spin-dependent electronic current flowing laterally through the In$_{0.53}$Ga$_{0.47}$As/In$_{0.52}$Al$_{0.48}$As double quantum well (DQW) structure, where the values of the Rashba spin-orbit parameter $\alpha_{\rm R}$ are opposite in sign but equal in magnitude between the constituent quantum wells [1]. By tuning the channel length of DQW and the magnitude of the externally applied in-plane magnetic field, one can block the transmission of one spin (e.g., spin-up) component, enabling us to obtain a spin-polarized current. Our experimental progress toward realizing the proposed device is also reported [2]. [1] T. Matsuura, S. Faniel, N. Monta, and T. Koga, Physica E {\bf 42}, 2707 (2010). [2] T. Koga, T. Matsuura, S. Faniel, S. Souma, S. Mineshige, Y. Sekine, and H. Sugiyama, IEICE Trans. Electron. {\bf E95-C}, 770 (2012). [Preview Abstract] |
Wednesday, March 20, 2013 12:39PM - 12:51PM |
N18.00006: Spin-orbit edge states in semiconductor two-dimensional systems L.L. Xu, Shaola Ren, J.J. Heremans, Djordje Minic, C.K. Gaspe, S. Vijeyaragunathan, T.D. Mishima, M.B. Santos The electromagnetic duality between the Aharonov-Casher and the Aharonov-Bohm topological phases can lead to magnetoelectronic edge effects in two-dimensional systems. Based on this duality, we propose and experimentally explore a quantized Hall effect in which magnetization transport may be quantized analogously to charge transport. When the magnetic moment is fully projected, the edge effect is a magnetization dual to the integer quantum Hall effect. An analogy also exists between this dual and the bosonic quantum Hall effect currently under investigation. In experiments we search for edge states induced by the equivalent vector potential from Rashba-type spin-orbit interaction. We use mesoscopic side-gated channel structures on InGaAs/InAlAs heterostructures where backscattering between edge states can experimentally form evidence for edge states. The side-gate voltage varies the effective gauge field and resistance as function of side-gate voltage is measured across the mesoscopic structures at either low applied magnetic field or at fixed magnetic filling factors to obtain states of defined spin (DOE DE-FG02-08ER46532, NSF DMR-0520550). [Preview Abstract] |
Wednesday, March 20, 2013 12:51PM - 1:03PM |
N18.00007: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 1:03PM - 1:15PM |
N18.00008: ABSTRACT WITHDRAWN |
Wednesday, March 20, 2013 1:15PM - 1:27PM |
N18.00009: Antilocalization, quantum coherence and spin coherence in quasi-one-dimensional GaAs/AlGaAs hole wires Shaola Ren, J.J. Heremans, M. Shayegan Antilocalization is measured in quasi-1D (Q1D) lithographic wires fabricated on a GaAs/AlGaAs 2D hole system. Shubnikov-de Haas oscillations show substantial spin-orbit interaction in the asymmetric quantum well. A set of 10 Q1D wires of length 20 $\mu$m and conducting width 300 nm were fabricated. Mobility and density are preserved in the wires, which show predominantly specular boundary scattering, indicating high quality hole wires. Antilocalization is present in both the wires and the unpatterned system, confirming the existence of spin-orbit interaction. The spin and phase coherence times are measured as functions of temperature by fitting the magnetoconductance to antilocalization theory. Q1D antilocalization theory, as used on InSb and InAs wires, does not fit the hole wires well, likely due to a combination of ballistic transport and strong spin-orbit interaction not fully accounted for theoretically. For both wires and unpatterned system the measurements still indicate the spin coherence times and the phase coherence times with the expected temperature dependence. The measurements allow a comparison of the spin coherence times, and of their lengthening under dimensional confinement, with observations on other spin-orbit coupled 2D systems. [Preview Abstract] |
Wednesday, March 20, 2013 1:27PM - 1:39PM |
N18.00010: The influence of the spin-orbit effect on the 0.7-anomaly: a functional renormalization group approach Olga Goulko, Florian Bauer, Jan Heyder, Jan von Delft In addition to plateaus at integer values of $G_0 = 2e^2/h$, the linear conductance of a quantum point contact shows an anomalous shoulder at around $0.7G_0$ -- the so-called 0.7-anomaly. Although the dependence of the 0.7-anomaly on parameters such as the temperature, the magnetic field, the bias voltage etc. has been widely studied, little is known about the influence of spin-orbit effects. We present a microscopic theory for the 0.7-anomaly, based on a one-dimensional tight binding model with a local on-site interaction, a smooth potential barrier and a homogeneous magnetic Zeeman field. In addition, we introduce Rashba and Dresselhaus terms into the Hamiltonian to capture the effect of spin-orbit coupling. We use a functional renormalization group approach to calculate the influence of interactions on the conductance at zero temperature. In this talk we present our theoretical predictions for the shape of the conductance curve, which depends strongly on the angle of the magnetic field if spin-orbit coupling is present. We also provide a detailed microscopic explanation of how the interplay of the magnetic field, the interaction and the spin-orbit coupling influences the conductance. [Preview Abstract] |
Wednesday, March 20, 2013 1:39PM - 1:51PM |
N18.00011: Microscopic Origin of the 0.7-Anomaly in Quantum Point Contacts J. von Delft, F. Bauer, J. Heyder, E. Schubert, D. Borowski, D. Taubert, B. Bruognolo, D. Schuh, W. Wegscheider, S. Ludwig Despite the simple structure of quantum point contacts, their conductance properties exhibit anomalous features, collectively known as the ``0.7-anomaly'', whose origin is still subject to controversial discussions. We offer a detailed microscopic explanation for the 0.7-anomaly and the zero-bias peak that typically accompanies it: the common origin of both is a smeared van Hove singularity in the local density of states at the bottom of the lowest one-dimensional subband of the point contact, which causes an anomalous enhancement in the Hartree potential barrier, magnetic spin susceptibility and inelastic scattering rate. We present theoretical calculations and experimental results that show good qualitative agreement for the dependence of the conductance on gate voltage, magnetic field, temperature, bias voltage (including the zero-bias peak) and interaction strength. For low field and temperature we predict and observe Fermi-liquid behavior analogous to that known for the Kondo effect in quantum dots. At high energies, however, the analogy between 0.7-anomaly and Kondo effect ceases to be applicable. [Preview Abstract] |
Wednesday, March 20, 2013 1:51PM - 2:03PM |
N18.00012: Tunable All Electric Spin Polarizer Using A Quantum Point Contact With Two Pairs of In-Plane Side Gates Nikhil Bhandari, James Charles, Maitreya Dutta, Partha Das, Marc Cahay, Richard Newrock, Steven Herbert We report the first experimental investigation of a device consisting of a quantum point contact (QPC) with four gates -- two in-plane side gates in series. The first set of gates (nearest the source contact) is asymmetrically biased to create spin polarization in the channel of the QPC. A symmetric bias is then applied on the second set of side gates (nearest the drain) and varied to tune the location of a conductance anomaly near 0.5 (x2e$^{2}$/h). The experimental results compare well with simulations of the four-gate QPC devices using a Non-Equilibrium Green's Function formalism. The device is shown to be a tunable all-electric spin polarizer. The range of common-mode bias on the first set of gates over which maximum spin polarization can be achieved is much broader for the four-gate structure compared with the case of a QPC with a single pair of in-plane side gates. [Preview Abstract] |
Wednesday, March 20, 2013 2:03PM - 2:15PM |
N18.00013: ABSTRACT WITHDRAWN |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700