Bulletin of the American Physical Society
APS March Meeting 2013
Volume 58, Number 1
Monday–Friday, March 18–22, 2013; Baltimore, Maryland
Session W18: Focus Session: Spin-Dependent Phenomena in Semiconductors - Dynamic and Nuclear Effects |
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Vanessa Sih, University of Michigan Room: 320 |
Thursday, March 21, 2013 2:30PM - 2:42PM |
W18.00001: THz Magneto-photoresponse of an InAs-based Quantum Point Contact Structure in the Region of Cyclotron Resonance Mehdi Pakmehr, Vincent Whiteside, Nikhil Bhandari, Marc Cahay, Richard Newrock, Bruce McCombe We have studied the THz magneto-photoresponse of a 2DEG in an InAs quantum well with an embedded Quantum Point Contact in the frequency/field region where electron cyclotron resonance (CR) dominates the response suing several lines from an optically pumped THz laser. The photoresponse near CR is manifested as an envelope of the amplitude of the Shubnikov-de Haas oscillations of the 2DEG with a peak near the CR field. Clear spin-splitting of the quantum oscillations is observed for B \textgreater\ 4, while the SdH oscillations do not show resolved spin-splitting up to 10 T. Data were simulated by a model of resonant carrier heating (due to CR), and from the simulations the carrier density, the CR effective mass, scattering times and the g-factor were obtained. We find a significantly enhanced g-factor, apparently due to many-electron exchange interaction effects. The g-factor determined from fitting spin-split Landau level peaks increases with magnetic field. Work at UB was supported by NSF DMR 1008138 and the Office of the Provost; work at the University of Cincinnati was supported by NSF ECCE 1028483. [Preview Abstract] |
Thursday, March 21, 2013 2:42PM - 2:54PM |
W18.00002: Terahertz excitation and control of spin photocurrents in a semiconductor nanostructure Nelson Studart, Anibal Bezerra, Leonardo Castelano, Paulo Farinas, Marcelo Maialle, Marcos Degani Time dependent calculations of induced photocurrents are presented for ZnMnSe semiconductor nanostructures under the action of a static magnetic field of a few Tesla. The study shows the existence of spectral domains in the THz range for which the spin polarization in the photocurrent is strongly sensitive to static biases applied in the growth direction of the structures. For such photon frequencies, changing the bias is predicted to reverse the spin polarization quite effectively for specific absorption frequencies. This behavior suggests the possibility of conveniently simple mechanisms for switching and torque generation. The physics underlying these results is studied and understood in terms of the spin dependent profiles of the structures. [Preview Abstract] |
Thursday, March 21, 2013 2:54PM - 3:06PM |
W18.00003: Anomalous spin precession and spin Hall effect in semiconductor quantum wells Peiru He, Xintao Bi, E.M. Hankiewicz, R. Winkler, Giovanni Vignale, Dimitrie Culcer We study the contributions of the anomalous position operator to the spin-Hall effect in quasi two-dimensional semiconductor quantum wells with strong band structure spin-orbit interactions. The skew scattering and side-jump \textit{scattering} terms in the SHE vanish, but we identify two additional terms in the SHE due to the anomalous position operator. One term reflects the modification of the spin precession due to the action of the external electric field, which produces an effective magnetic field perpendicular to the plane of the quantum well. The other term reflects a similar modification of the spin precession due to the action of the electric field created by random impurities. We refer to these two effects collectively as \textit{anomalous spin precession}. In electron systems with weak momentum scattering, anomalous spin precession due to the external electric field equals 1/2 the side-jump SHE, while the additional impurity-dependent contribution depends on the form of the band structure SO coupling. For band structure SO linear in wave vector the two additional contributions cancel. For band structure SO cubic in wave vector external electric field contribution can be detected through its density dependence. In 2D hole systems both additional contributions vanish. [Preview Abstract] |
Thursday, March 21, 2013 3:06PM - 3:18PM |
W18.00004: Electrically generated nuclear spin polarization in In$_{.04}$Ga$_{.96}$As Christopher Trowbridge, Benjamin Norman, Yuichiro K. Kato, David Awschalom, Vanessa Sih The promises of lower power consumption and simple interfacing to magnetic storage has driven interest in the development of spintronics, in which devices could take advantage of electron spin as a means to store, move, and process data. Due to its long lifetime in moderate fields, nuclear polarization could serve as intermediate timescale data storage in both classical spintronic and quantum computation schemes. Here, we investigate the role of nuclear spins in materials with electrically driven spin polarization. The electron spin polarization generated by electrical current in a non-magnetic semiconductor is transferred via dynamic nuclear polarization to the nuclei. The resulting nuclear field is interrogated using Larmor magnetometry. We measure nuclear field as a function of current, applied magnetic field, and temperature. Polarization decay dynamics and the role of nuclei in devices are also discussed. [Preview Abstract] |
Thursday, March 21, 2013 3:18PM - 3:30PM |
W18.00005: Knight shift and quadrupolar relaxation measured by NMR in Fe/GaAs heterostructures Kevin Christie, Chad Geppert, Mun Chan, Qi Hu, Chris Palmstr\"{o}m, Paul Crowell We report on all-electrical measurements of nuclear magnetic resonance (NMR) in epitaxial (100) Fe/GaAs heterostructures with a channel doping (Si) of $n =5\times 10^{16}$~cm$^{-3}$. By changing the electrical bias, measurements of NMR were performed as a function of spin accumulation. A Knight shift due to the presence of spin-polarized electrons is demonstrated under conditions of large (10-20\%) spin polarization. The effects of nuclear quadrupole moments are also investigated. Although GaAs is cubic, strain induced field gradients split the NMR line into quadrupole multiplets. We investigate the role of nuclear quadrupole relaxation as a function of temperature. Phonon induced quadrupolar relaxation is expected to increase strongly with temperature and be more pronounced for the As nuclei. We show that the evolution of the relative magnitude of the NMR peaks as a function of temperature agrees well with a model dominated by quadrupole relaxation. Supported by NSF DMR-0804244 and DMR-1104951. [Preview Abstract] |
Thursday, March 21, 2013 3:30PM - 3:42PM |
W18.00006: Long-lived electron spins in a modulation doped (100) GaAs quantum well John Colton, David Meyer, Ken Clark, Daniel Craft, Jane Tanner, Tyler Park, Phil White We have measured $T_1$ spin lifetimes of a 14 nm modulation-doped (100) GaAs quantum well using a time-resolved pump-probe Kerr rotation technique. The quantum well was selected by tuning the wavelength of the probe laser. $T_1$ lifetimes in excess of 1 microsecond were measured at 1.5 K and 5.5 T, exceeding the typical $T_2^*$ lifetimes that have been measured in GaAs and II-VI quantum wells by orders of magnitude. We observed effects from nuclear polarization, which were largely removable by simultaneous nuclear magnetic resonance, along with two distinct lifetimes under some conditions that likely result from probing two differently-localized subsets of electrons. [Preview Abstract] |
Thursday, March 21, 2013 3:42PM - 4:18PM |
W18.00007: Spin-orbit ferromagnetic resonance Invited Speaker: Andrew Ferguson In conventional magnetic resonance techniques the magnitude and direction of the oscillatory magnetic field are (at least approximately) known. This oscillatory field is used to probe the properties of a spin ensemble. Here, I will describe experiments that do the inverse [1]. I will discuss how we use a magnetic resonance technique to map out the current-induced effective magnetic fields in the ferromagnetic semiconductors (Ga,Mn)As and (Ga,Mn)(As,P). These current-induced fields have their origin in the spin-orbit interaction [2-4]. Effective magnetic fields are observed with symmetries which resemble the Dresselhaus and Rashba spin-orbit interactions and which depend on the diagonal and off-diagonal strain respectively. Ferromagnetic semiconductor materials of different strains, annealing conditions and concentrations are studied and the results compared with theoretical calculations. Our original study measured the rectification voltage coming from the product of the oscillatory magnetoresistance, during magnetisation precession, and the alternating current. More recently we have developed an impedance matching technique which enables us to extract microwave voltages from these high resistance (10 k$\Omega )$ samples [5]. In this way we measure the microwave voltage coming from the product of the oscillating magneto-resistance and a direct current. The direct current is observed to affect the magnetisation precession, indicating that anti-damping as well as field-like torques can originate from the spin-orbit interaction. \\[4pt] [1] D. Fang et al. Nat. Nano. 6, 413 (2011).\\[0pt] [2] A. Chernyshov et al. Nat. Phys. 5, 656 (2009).\\[0pt] [3] A. Manchon and S. Zhang Phys. Rev. B 79, 094422 (2009).\\[0pt] [4] I. Garate and A. H. MacDonald Phys. Rev. B 80, 134403 (2009).\\[0pt] [5] D. Fang et al. Appl. Phys. Lett. 101, 182402 (2012). [Preview Abstract] |
Thursday, March 21, 2013 4:18PM - 4:30PM |
W18.00008: Experimental demonstration of Scanned Spin-Precession Microscopy V.P. Bhallamudi, C.S. Wolfe, V.P. Amin, D.E. Labanowski, A.J. Berger, D. Stroud, J. Sinova, P.C. Hammel We present the demonstration of a new spin-microscopy tool that relies on the precessional response of spins to the spatially heterogeneous field of a micromagnet. In this first experiment, we map the spin density within an optically pumped GaAs sample by recording the variations of a global spin-photoluminescence signal as a function of a micromagnetic probe's position (relative to the pump beam). The spin density map is then obtained by deconvolving the measured signal with an experimentally or theoretically determined response of the spins to their magnetic environment. The response function is sensitive to other important properties, such as spin lifetime and gyromagnetic ratio, and thus these properties can also imaged. Further, the technique can be employed in conjunction with both optical and electrical detection schemes. In the former case it can enhance the imaging resolution while for the latter it can enable imaging. Due to the magnetic nature of coupling between the probe and the spins, this technique has the potential to be material independent and enable subsurface imaging. [Preview Abstract] |
Thursday, March 21, 2013 4:30PM - 4:42PM |
W18.00009: Spin relaxation near the metal-insulator transition: dominance of the Dresselhaus spin-orbit coupling Pablo I. Tamborenea, Guido A. Intronati, Dietmar Weinmann, Rodolfo A. Jalabert We identify the Dresselhaus spin-orbit coupling as the source of the dominant spin-relaxation mechanism in the impurity band of a wide class of n-doped zincblende semiconductors. The Dresselhaus hopping terms are derived and incorporated into a tight-binding model of impurity sites, and they are shown to unexpectedly dominate the spin relaxation, leading to spin-relaxation times in good agreement with experimental values. This conclusion is drawn from two complementary approaches: an analytical diffusive-evolution calculation and a numerical finite-size scaling study of the spin relaxation time. Reference: G. A. Intronati, P. I. Tamborenea, D. Weinmann, and R. A. Jalabert, Phys. Rev. Lett. vol. 108, 016601 (2012). [Preview Abstract] |
Thursday, March 21, 2013 4:42PM - 4:54PM |
W18.00010: X-Ray Circular Dichroism Detected Spin Populations in N Doped (100) GaAs Sioan Zohar, Jong Woo Kim, Philip Ryan, David Keavney We present the x-ray absorption and reflectivity of optically injected spin populations into highly doped n:GaAs. The spin population was excited in the GaAs using a circularly polarized laser at the band gap energy and detected using synchronous methods referenced to the x-ray repetition rate and laser chopping frequency. We observe x-ray circular dichroism along the Ga L$_{3}$ and L$_{2}$ edges two orders of magnitude larger than expected from LMTO band structure calculations. This observation is explained in the context of a surface related spin dependent non-equilibrium population immediately above and below the GaAs band-gap. [Preview Abstract] |
Thursday, March 21, 2013 4:54PM - 5:06PM |
W18.00011: Mott's scattering and Spin Hall Effect modeled by means of numerical solutions of the Schr\"{o}dinger equation Nagendra Dhakal, Mikhail Erementehouk, Michael Leuenberger We have developed a code for numerical solution of non-stationary Schr\"{o}dinger equations based on the finite difference time-domain (FDTD) method. We model the 2 dimensional free electron gas system using perfectly matched layers for the open surrounding space. We study the effect of localized impurities on the time evolution of the electron wave function, thereby observing dephasing introduced by the impurities. Our numerical simulations show the de-coherence due to the impurities at moderate impurity densities and Anderson localization at high impurity densities. We implement the code for studying an effect of the spin orbit interaction in presence of the impurities. The clear picture of Mott's scattering gives rise to the Spin Hall Effect. Our results are important for the implementation of quantum computing, quantum communication, and spintronics. [Preview Abstract] |
Thursday, March 21, 2013 5:06PM - 5:18PM |
W18.00012: Diode Aided Geometrical Enhancement of Magnetoresistance in Semiconductors Xiaozhong Zhang, Caihua Wan, Shaochu Luo, Jiming Wang, Jiaojiao Chen, Hongguang Piao Magnetoresistance (MR) reported in some non-magnetic semiconductors particularly silicon has triggered considerable interest owing to the large magnitude of the effect. Here we showed that MR in lightly doped n-Si can be significantly enhanced by introducing a diode in the device and proper design of the carrier path [1,2]. We designed an MR device whose room-temperature MR ratio reaching 30{\%} at 0.065T and 20000{\%} at 1.2T, respectively, approaching the performance of commercial MR devices. We also realized MR of over 2600{\%} in GaAs and Ge at 1.2T [2]. The MR mechanism of our devices is: The diode helps to establish a transition from low resistance state to high resistance state. In the transition region the small change in magnetic field cause a large change in MR. Because our MR device is based on a conventional Si/semiconductor platform, it should be possible to integrate it with existing Si/semiconductor devices and so aid the development of Si/semiconductor-based magneto-electronics leading to some multifunctional devices.\\[4pt] [1] Caihua Wan, Xiaozhong Zhang, et al.\textbf{,} Nature, \textbf{477}, 304 (2011).\\[0pt] [2] Xiaozhong Zhang, et al. Geometrical enhanced magnetoresistance in semiconductors (in submission) [Preview Abstract] |
Thursday, March 21, 2013 5:18PM - 5:30PM |
W18.00013: A spin-influenced hopping theory for transport in molecular semiconductors$\backslash $fs20 Chang-Qin Wu We investigate the influence of charge carrier's spin interaction on the hopping transport in molecular semiconductors. By considering the quenching of the spin correlation after the carrier's incoherent jump between molecules, we obtain the carrier's hopping rate that contains explicitly the contribution of carrier's spin interaction. As a consequence, the rate is modulated by applied magnetic field, leading to the magnetoresistance with a general feature of a Lorentzian-shape saturation at large fields and an ultrasmall-field component, which explains well the related experiments observed in organic semiconducting materials. [Preview Abstract] |
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