Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session H22: Focus Session: Optical Generation and Detection of Spins in Semiconductors |
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Sponsoring Units: GMAG DMP FIAP Chair: Jay Kikkawa, University of Pennsylvania Room: 324 |
Tuesday, March 17, 2009 8:00AM - 8:36AM |
H22.00001: ABSTRACT WITHDRAWN |
Tuesday, March 17, 2009 8:36AM - 8:48AM |
H22.00002: Coupling Mechanism of Anisotropic Interface and Bulk Magnetism in Thin Epitaxial Fe Film on AlGaAs (001) Yichun Fan, Haibin Zhao, Gunter Lupke, Aubrey Hanbicki, Connie Li, Berry Jonker A systematic study of the coupling mechanism of anisotropic interface and bulk magnetism in Fe/AlGaAs(001) heterostructures is carried out with different Fe film thicknesses. The uniaxial, cubic and out-of-plane anisotropy fields are determined for the interface and the bulk by time-resolved magnetization induced second harmonic generation (MSHG) and magneto-optic Kerr effect (MOKE), respectively. The experimental data show that the interface-induced uniaxial magnetic anisotropy is uniform within the first 5nm, but it decreases fast beyond this thickness. Moreover, the thickness of the Fe interface layer is estimated to be 1.7A (close to half of the Fe lattice constant), which is expected by MSHG theory. [Preview Abstract] |
Tuesday, March 17, 2009 8:48AM - 9:00AM |
H22.00003: Dynamic polarization of Mn spins coupled to vertical optical cavities G. Calusine, R.C. Myers, D.D. Awschalom Single magnetic spins in semiconductors can exhibit long lifetimes and are electrically controllable due to coupling of their spin states with those of the host semiconductor. In particular, Mn ions doped into GaAs quantum wells have spin lifetimes $\sim$10 nanoseconds and can be optically manipulated in zero magnetic field\footnote{R. C. Myers, M. H. Mikkelsen, J.-M. Tang, A. C. Gossard, M. E. Flatt\'{e}, and D. D. Awschalom, \textit{ Nature Materials} \textbf{7}, 203 (2008).}. To study this system in the low density limit, we incorporate a distributed Bragg reflector optical cavity around the Mn containing wells, which enhances Mn luminescence and allows spatial isolation of a small number of Mn ions imaged using scanning micro-photoluminescence. In such structures, we observe unusually long Mn T$_{2}^{\ast}> 60$ ns. We discuss the effect of cavity coupling on spin dynamics Mn ions in the single ion limit. [Preview Abstract] |
Tuesday, March 17, 2009 9:00AM - 9:12AM |
H22.00004: Generation and transport of photo-excited carriers in diamond F.J. Heremans, G.D. Fuchs, C.F. Wang, D.D. Awschalom, Ronald Hanson Photo-excited carrier transport in diamond has generated substantial interest in the past few years. The combination of high thermal conductivity, large band-gap, and large dielectric breakdown make diamond attractive in optoelectronic, high-power and high-frequency applications. Here we present measurements of electrical conduction by sub-band gap photo-excited carriers between metallic gates lithographically patterned on the surface of single-crystal type Ib diamond. The time-dependent charging and discharging photo-currents follow a ``stretched exponential'' form, which results from a trap state conduction mechanism mitigated by a local space charge. We also perform photo-excited magneto-transport as well as energy-dependant photo-conduction measurements to investigate the detailed origins of this sub-gap photo-excited conduction. [Preview Abstract] |
Tuesday, March 17, 2009 9:12AM - 9:24AM |
H22.00005: Excitation and doping dependence of hole-spin relaxation in bulk GaAs Michael Krauss, David Hilton, Hans Christian Schneider We present theoretical and experimental results on ultrafast hole-spin dynamics in bulk GaAs. By combining a sufficiently realistic bandstructure at the level of an 8$\times$8 $\vec{k} \cdot \vec{p}$ theory and a dynamical treatment of the relevant scattering mechanisms [1], we obtain quantitative agreement between the microscopic theoretical results and differential transmission measurements [2] for different excitation conditions. In particular, we examine the dependence of the hole-spin relaxation time on the optically excited carrier density, lattice temperature, and doping concentration. Although the spin relaxation is rather insensitive to changes in the optically excited density and temperature, strong p-doping causes a significantly faster relaxation. \newline [1] M. Krauss, M. Aeschlimann, and H. C. Schneider, Phys.Rev.Lett.\ \textbf{100}, 256601 (2008)\newline [2] D. J. Hilton and C. L. Tang, Phys.\ Rev.\ Lett. \textbf{89}, 146601 (2002) [Preview Abstract] |
Tuesday, March 17, 2009 9:24AM - 9:36AM |
H22.00006: Studies of electron spin lifetimes in InGaAs:Al quantum wells T. Ali, I. Khan, M. Yasar, A. Petrou, C. Li, A. Hanbicki, G. Kioseoglou, B. Jonker We have carried out optical pumping, Hanle and longitudinal Hanle studies of InGaAs:Al/GaAs single quantum wells. The circular polarization at zero magnetic field has a maximum around 50 K indicating that at low temperatures the recombination is associated with a bound electron. The measured spin lifetimes at low temperatures are an order of magnitude longer than those measured in reference GaAs/AlGaAs quantum wells. This is attributed to the suppression of the Dyakonov-Perel spin relaxation mechanism in this bound system. As the temperature is increased from 5 to 50 K the spin lifetimes decrease and become comparable to the lifetimes of the reference sample. In the longitudinal Hanle geometry the circular polarization increases with magnetic field and reaches a maximum at B $\approx $ 1.5 tesla. Beyond 1.5 tesla the circular polarization decreases. A series of polarization oscillations superimposed on the decreasing background with a periodicity of approximately 1 tesla is observed. These oscillations are tentatively attributed to the variations in the magnetic flux through the bound electron orbit. Work at SUNY was supported by ONR and NSF [Preview Abstract] |
Tuesday, March 17, 2009 9:36AM - 9:48AM |
H22.00007: Spontaneous Loss of Spin Coherence in GaAs/Si Heterostructure Guanglei Cheng, Patrick Irvin, Biqin Huang, Ian Appelbaum, Jeremy Levy We present a possible way to optically inject spins into silicon. In this work, GaAs and Silicon-on-Insulator (SOI) wafers are bonded together by an ultrathin Ag layer using UHV wafer bonding. Standard optical pump-probe Kerr microscopy technique is applied to examine the spin coherence in the GaAs/Si heterostructure. In some areas of the bonded wafer, a relatively long spin coherence time of T2*=0.5 ns is observed in the GaAs. In other parts of the sample, the spin coherence is observed to decay much more rapidly (T2*=140ps). One possible explanation is that the quality of the bond varies across the wafer and that the strongly bonded areas exhibit spin transport from GaAs to silicon. [Preview Abstract] |
Tuesday, March 17, 2009 9:48AM - 10:00AM |
H22.00008: Coherent optical control of correlation waves of spins in semiconductors Eran Ginossar, Yehoshua Levinson, Shimon Levit We calculate the dynamical fluctuation spectrum of electronic spins in a semiconductor under a steady-state illumination by light containing polarization squeezing correlations. Taking into account quasi-particle lifetime and spin relaxation for this non-equilibrium situation we consider up to fourth order optical effects which are sensitive to the squeezing phases. We demonstrate the possibility to control the spin fluctuations by optically modulating these phases as a function of frequency, leading to a non-Lorentzian spectrum which is very different from the thermal equilibrium fluctuations in n-doped semiconductors. Specifically, in the time-domain spin-spin correlation can exhibit time delays and sign flips originating from the phase modulations and correlations of polarizations, respectively. For higher light intensity we expect a regime where the squeezing correlations will dominate the spectrum. [Preview Abstract] |
Tuesday, March 17, 2009 10:00AM - 10:12AM |
H22.00009: Time Resolved Spectroscopy of InSb Quantum Wells Using Differential Transmission Technique K. Nontapot, M. Bhowmick, G.A. Khodaparast, S.J. Chung, M.B. Santos The growing interest in spin-related phenomena and devices has prompted intense activity in the science and engineering of narrow gap semiconductors (NGS). NGS offer several scientifically unique features such as small effective masses, large g-factors, high intrinsic mobilities, and large spin- orbit coupling effects. In this work we report the dynamics of photo-excited carrier/spin in several InSb/ Al$_{x}$In$_{1-x} $Sb based quantum wells (QWs) using differential transmission spectroscopy. The InSb QW layers were selectively pumped and probed by mid-infrared pulses to avoid possible contributions from the barrier materials. We compare our results with the earlier measurements using magneto-optical Kerr (MOKE) effect. Our results are important to understand different relaxation mechanisms in NGS with strong-spin orbit interactions. [Preview Abstract] |
Tuesday, March 17, 2009 10:12AM - 10:24AM |
H22.00010: Spin polarized current in InSb based structures M. Frazier, M. Bhowmick, J.J. Heremans, G.A. Khodaparast, S.J. Chung , M.B. Santos, X. Liu, J. Furdyna Recently, there has been much interest in developing and exploring spin based semiconductor devices and phenomena. One of the key challenges in developing spin based devices is to generate, control, and measure spin currents directly. In this talk, we report interband circular photogalvanic (CPG) effects using pulsed near-infrared radiation in InSb quantum wells and two InSb films grown on GaAs and InP substrates. We observe a CPG current whose direction and magnitude depend on the helicity of the incident light, the angle of incidence, and temperature. Our observation is important to understand zero- field spin splitting mechanisms in a system with strong spin- orbit interaction. [Preview Abstract] |
Tuesday, March 17, 2009 10:24AM - 10:36AM |
H22.00011: Optically-Induced $^{13}$C Nuclear Spin Polarization through Nitrogen-Vacancy Centers in Diamond Jonathan King, Patrick Coles, Jeffrey Reimer The spin-1 negatively charged nitrogen-vacancy (NV) center in diamond has received much attention for its long spin-coherence times and optical polarization into the m$_{s}$=0 sublevel. These properties make it attractive for applications such as quantum information processing and high-resolution magnetometry. Large nuclear polarizations in diamond may be useful to quench decoherence, as an initialization step for quantum computing, or as a platform for enhancement of nuclear magnetic resonance (NMR) signal in dilute spin systems. In this work, we demonstrate the polarization of the bulk $^{13}$C nuclear spin system by interaction with the optically polarized NV center system at 9.4 Tesla and 5K nominal temperature. Large nuclear polarizations are observed through Faradaic detection of bulk $^{13}$C NMR signals. The signals are opposite in sign to thermally-generated signals, indicating nuclear polarization into the m$_{I}$ = -1/2 sublevel. We model the phenomenon and propose microscopic mechanism for the polarization. [Preview Abstract] |
Tuesday, March 17, 2009 10:36AM - 10:48AM |
H22.00012: Optical hyperpolarization of the nuclear and electronic spins of $^{31}$P in $^{28}$Si A. Yang, M. Steger, T. Sekiguchi, M. L. W. Thewalt, T. D. Ladd, K. M. Itoh, H. Riemann, N. V. Abrosimov, P. Becker, H.-J. Pohl, J. W. Ager III, E. E. Haller We have recently shown that the donor hyperfine splitting can be resolved for the $^{31}$P donor bound exciton transition in highly enriched $^{28}$Si, enabling either optical or optical-electrical readout of the electronic and nuclear spin state of this promising qubit candidate.[1] Here we show that these same optical transitions can be used to quickly achieve large nuclear and electronic hyperpolarizations of the $^{31}$P donor in $^{28}$Si. This may provide a viable solution to the problem of initializing the nuclear spins, a roadblock for quantum computing schemes involving nuclear spins in Si. We also report on the remarkably narrow homogeneous linewidth of this bound exciton transition, measured by hole burning spectroscopy. This suggests that even higher spin selectivity and hyperpolarization may be achievable in more highly enriched $^{28}$Si, or when dealing with individual $^{31}$P donors. [1] A. Yang et al., Phys. Rev. Lett. \underline {97}, 227401 (2006). [Preview Abstract] |
Tuesday, March 17, 2009 10:48AM - 11:00AM |
H22.00013: Time-resolved Infrared Magnetospectroscopy of GaAs at the NSLS G.L. Carr, J.J. Tu We describe a facility for performing photo-induced time-resolved infrared spectroscopy of materials in magnetic fields up to 10T at beamline U4IR of the National Synchrotron Light Source (NSLS). The facility combines an existing time-resolved capability (based on pulsed synchrotron radiation and a synchronized Ti:sapphire laser to achieve $\sim $100 ps resolution) with a split-coil superconducting solenoid and optical cryostat. We also report a THz study of photocarrier and exciton dynamics in GaAs using this facility. It is found that, for B$>$0, a portion of the photo-induced carrier absorption appears as an electron cyclotron resonance, while the exciton unbinding absorption splits into spin and orbital transitions (Zeeman effect). At low temperatures, we observe that the relaxation of photocarriers toward the band edge involves the breaking of existing excitons, leading to a combination of absorption and bleaching features that evolve on a $\sim $1 ns time scale. [Preview Abstract] |
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