Bulletin of the American Physical Society
2006 APS March Meeting
Monday–Friday, March 13–17, 2006; Baltimore, MD
Session W19: Focus Session: Semiconductor Spin Transport: Noise/Theory |
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Sponsoring Units: GMAG DMP Chair: Gerrit Bauer, TU Delft Room: Baltimore Convention Center 316 |
Thursday, March 16, 2006 2:30PM - 2:42PM |
W19.00001: Shot noise and s-o coherent control of entangled and spin polarized electrons. J. Carlos Egues, Guido Burkard, Daniel Saraga, John Schliemann, Daniel Loss We extend our previous work on shot noise for entangled and spin polarized electrons in a beam-splitter geometry with spin-orbit (s-o) interaction in the incoming leads. Besides accounting for both the Dresselhaus and the Rashba spin-orbit terms, we present general formulas for the shot noise of singlet and triplets states derived within the scattering approach. We determine the full scattering matrix of the system for the case of leads with two orbital channels coupled via a weak s-o interaction inducing channel anti-crossings. We show that this interband coupling gives rise to an additional modulation angle which allows for further coherent control of the electrons. We also derive explicit shot noise formulas for a variety of correlated pairs (e.g., Bell states) and lead spin polarizations. Interestingly, the singlet and $\backslash $textit{\{}each{\}} of the triplets defined along the quantization axis perpendicular to lead 1 and in the plane of the beam splitter display distinctive shot noise for injection energies near the channel anti-crossings -- one can tell apart all the triplets through noise measurements. Finally, we find that backscattering within lead 1 reduces the visibility of the noise oscillations. This work was supported by NCCR Nanoscale Science, EU-Spintronics, CNPq, Swiss NSF, DARPA, ARO, and ONR (to appear in PRB). [Preview Abstract] |
Thursday, March 16, 2006 2:42PM - 2:54PM |
W19.00002: Shot Noise of a Quantum Point Contact Yiming Zhang, Leonardo DiCarlo, Douglas McClure, David Reilly, Charles Marcus, Loren Pfeiffer, Ken West We report detailed simultaneous measurements of shot noise and DC transport in a quantum point contact (QPC) as a function of source-drain bias, gate voltage and in-plane magnetic field. The magnetic field evolution of the 0.7 feature in both conductance and noise is clearly visible and is compared to a simple model, giving good quantitative agreement. [Preview Abstract] |
Thursday, March 16, 2006 2:54PM - 3:06PM |
W19.00003: Theory of spin noise spectroscopy of itinerant fermions Simon Kos, Alexander Balatsky, Scott Crooker, Peter Littlewood, Dwight Rickel, Darryl Smith We study the noise of spin magnetization in a region within a system of fermions in different regimes of temperature (degenerate/non-degenerate) and disorder (ballistic/diffusive), with and without spin-flip processes included, and with no particle-particle interactions. We obtain a single spectral line, analyze the dependence of its width and spectral weight on the parameters of the system and the size of the region of interest, and discuss conditions for the maximal effect. We compare our results to the recent measurements of spin noise of alkali-gas vapor and of conduction electrons in a GaAs epilayer. [Preview Abstract] |
Thursday, March 16, 2006 3:06PM - 3:18PM |
W19.00004: Spin-resolved shot noise in multichannel spin-orbit coupled quantum wires Ralitsa Dragomirova, Branislav Nikoli\'c The characterization of spin-dependent transport via shot noise has recently attracted considerable attention in semiconductor spintronics. The key quantity that makes it possible to obtain the shot noise of both spin currents and spin-polarized charge currents is the correlation function between the spin-resolved charge currents. We extend the Landauer-B\"uttiker scattering formalism to obtain the spin-resolved shot noise for arbitrary polarization of the injected current and apply it to two-probe multichannel quantum wire with the Rashba spin-orbit interaction. We find that the Fano factor of the charge shot noise is non-zero even for ballistic transport and increases with the strength of the Rashba spin-orbit coupling due to enhancement of the backscattering at the lead-wire interface. In disordered quantum wires this effect enhances the Fano factor beyond the standard $F=1/3$ shot noise suppression. [Preview Abstract] |
Thursday, March 16, 2006 3:18PM - 3:30PM |
W19.00005: Valley-Kondo Effect in Transport Through a Silicon Quantum Dot Shiueyuan Shiau The Anderson model is applied to transport through a silicon quantum dot with infinite Coulomb interaction U with the valley degeneracy taken into account. At zero temperature, we study the conductance in the Kondo regime as a function of applied magnetic field, using the variational method developed by Gunnarsson and Sch\"{o}nhammer. The conductance peaks show a characteristic evolution due to the interplay of Zeeman splitting and valley splitting. [Preview Abstract] |
Thursday, March 16, 2006 3:30PM - 3:42PM |
W19.00006: Time-dependent multiple scattering approach for a single finger-gate in a Rashba-type quantum channel . Lu-Yao Wang We consider a Rashba-type quantum channel (RQC) consisting of one AC-biased finger-gates (FG) that orient perpendicularly and located above the RQC. Such an AC-biased FG gives rise to a local time-modulation in the Rashba coupling parameter, and generates a dc spin current (SC). A static potential is located inside or outside the FG in the RQC and the backscattering effect is studied. We use analytical time-dependent multiple scattering approach to treat the effect of the SC suppression due to a static potential in the RQC. [Preview Abstract] |
Thursday, March 16, 2006 3:42PM - 3:54PM |
W19.00007: Spin-current detector by a periodic array of quantum dots with Rashba Hamiltonian Jun-Qiang Lu, X.-G. Zhang, Sokrates T. Pantelides Electron diffraction by a periodic array of quantum dots is studied using the Rashba Hamiltonian and a plane wave-based Green function method. A transverse charge current is found due to the asymmetric spatial diffraction of a spin-polarized electron injection. The spin-polarization of the forward electon current is maintained after passing through the array. Such an array can be used as a non-magnetic spin-current detector. Detailed results in terms of the parameters relevant to experimental design, such as the size of the quantum dots, strength of the spin-orbit coupling, are presented. [Preview Abstract] |
Thursday, March 16, 2006 3:54PM - 4:06PM |
W19.00008: Effect of Coulomb interaction on the spin-galvanic mode in a two dimensional electron gas with Rashba spin-orbit interaction. Gernot Guntherodt, Yaroslaw B. Bazaliy, Stuart S. P. Parkin, B. V. Bazaliy Recently a new propagating mode of coupled charge and spin oscillations was predicted in a two dimensional electron gas with a sufficiently strong Rashba interaction. We show [cond-mat/0511534] that Coulomb interaction qualitatively modifies the spectrum and increases the characteristic wavelength of this mode by orders of magnitude, but does not suppress it. An absorption experiment that can conclusively detect the presence or absence of such a propagating mode is proposed. [Preview Abstract] |
Thursday, March 16, 2006 4:06PM - 4:18PM |
W19.00009: Quantum coherence oscillations in InSb and InAs J.A. Peters, Hong Chen, J.J. Heremans, N. Goel, S.J. Chung, M.B. Santos, W. Van Roy, G. Borghs Quantum oscillation phenomena in parallel arrays of loops have been investigated in InSb/AlInSb and InAs/AlGaSb heterostructures, notable for their strong spin-orbit interaction. The arrays consist of parallel lines of hexagonal lattice cells, forming linear concatenations of loops. From the h/2e periodicity, the dominance of Altshuler-Aronov-Spivak (AAS) oscillations is deduced. Measurement of the temperature dependence of the oscillations enables the extraction of spin and phase coherence lengths in InSb and InAs. The spin coherence lengths show a weak drop with increasing temperature, akin to the mobility mean free path behavior, and consistent with a dominant Elliott-Yafet related spin relaxation mechanism in both heterostructures. The phase coherence lengths follow a power law without observed saturation at the lowest temperatures. NSF DMR-0094055 (JJH), DMR-0080054, DMR-0209371 (MBS). [Preview Abstract] |
Thursday, March 16, 2006 4:18PM - 4:30PM |
W19.00010: Rashba spin-orbit and lateral local confinement effects in quasi-two-dimensional electronic systems Gabriele Giuliani, Stefano Chesi We consider the effects of lateral confinement on a two dimensional electron gas in the presence of different types of spin-orbit coupling as applied to the electrons and holes in $GaAs$ heterostructures. Both the linear and cubic Rashba spin-orbit coupling mechanisms have been studied. We show that confinement leads to interesting spin polarization effects that can in principle be observed by transport measurements across a quantum point contact. [Preview Abstract] |
Thursday, March 16, 2006 4:30PM - 4:42PM |
W19.00011: Response Functions and Collective Oscillations of a Two Dimensional Electron Gas in the Presence of Rashba Spin-Orbit Coupling George Simion, Gabriele F. Giuliani Various response functions and the spectrum of the collective excitations of a two dimensional electron liquid in the presence of Rashba type spin-orbit coupling have been studied within time dependent mean field formalism. Of particular interest are the results concerning the in-plane and out-of- plane spin susceptibility of the paramagnetic phase and the corresponding spin excitations. As an by product of this analysis we have derived an exact analytical expression for the static density response function which corrects formulas previously appeared in the literature. Approximate analytical expressions have also be derived for the low frequency, long wave length dependence of the same function. [Preview Abstract] |
Thursday, March 16, 2006 4:42PM - 4:54PM |
W19.00012: Mean field phase diagram of a two dimensional electron liquid with Rashba spin-orbit Stefano Chesi, Gabriele Giuliani By a combination of analytic an numerical techniques we have mapped out the mean field phase diagram of a two dimensional electron liquid in the presence of Rashba or Dresselhaus spin-orbit. Although inhomogeneous solutions can be found that minimize the total energy, we have carried out a systematic study of the spatially homogeneous phases in the $(r_s, \alpha)$ diagram (with $r_s$ the density parameter and $\alpha$ the strength of the spin-orbit coupling). The scenario is intriguing for a number of broken symmetry states have been unraveled that can be characterized by suitable momentum space occupation numbers $n_{\bf k}$ and local spin quantization axes $\hat{s}_{\bf k}$. While at high densities the system is as expected paramagnetic, at lower densities (or larger $\alpha$ values) markedly different ferromagnetic phases exist with spontaneous polarization oriented perpendicular or parallel to the plane of motion that are characterized by non trivial spin textures in momentum space. Of particular interest is a phase transition between an isotropic paramagnetic state to an anisotropic ferromagnetic one that occurs in the large $\alpha$ limit. The relation between the various phase transitions and the differential instabilities signaled by the in plane and out of plane spin susceptibilities will be discussed. [Preview Abstract] |
Thursday, March 16, 2006 4:54PM - 5:06PM |
W19.00013: Cubic Dresselhaus Spin Orbit Coupling in Small Quantum Dots Jacob J. Krich, Bertrand I. Halperin Due to the suppression of linear spin-orbit effects in small quantum dots in two-dimensional electron systems, the cubic Dresselhaus spin-orbit coupling can play a significant role in such phenomena as the variance of conductance through a dot. We characterize the different spin-orbit coupling terms by the strength of the anti-crossings they induce in the eigenstates of a closed quantum dot as an in-plane magnetic field is increased, and we perform numerical simulations in a chaotic billiard model to estimate the RMS anti-crossing energy. We investigate the conditions under which the cubic Dresselhaus effects may be measurable and significant for realizable dot configurations. [Preview Abstract] |
Thursday, March 16, 2006 5:06PM - 5:18PM |
W19.00014: g-factor anisotropy in p-type GaAs/AlGaAs quantum point contacts Sunanda Koduvayur, Leonid Rokhinson In this work we report the influence of lateral confinement on the effective Lande \textbf{g}-factor for holes in GaAs. For 2D hole gas grown along crystallographic direction other than the high symmetry [100] or [111], mixing of heavy and light hole subbands leads to anisotropic g-factor depending on the direction of the in-plane magnetic field.Further lateral confinement of the holes into 1D channel modifies g-factor depending on the strength and direction of the confining potential. We investigate \textbf{g}-factor in quantum point contacts (QPC) fabricated on 2D hole gas on [$\bar {3}11$]A GaAs by AFM lithography using the local anodic oxidation technique. Several QPCs are oriented along the major [$\bar {2}33$] or [$\bar {1}10$] axis. In-plane \textbf{B} is predominantly acting on the spin part of the Hamiltonian and the magnitude of the Zeeman splitting can be obtained from energy level spectroscopy combined with the critical fields at which half-integer steps in the conductance (in units of $\frac{2e^2}{h})$ appear. The \textbf{g}-factor is found to be strongly modified compared to the values reported for a 2D hole gas and has strong dependence on the quantized momentum normal to the current flow (number of filled energy levels in the point contact). Thus the g-factor can be modulated electrostatically, providing an extra degree of control of spintronic devices. [Preview Abstract] |
Thursday, March 16, 2006 5:18PM - 5:30PM |
W19.00015: The effect of interactions on the geometrical structure of the Fermi surface in systems with spin-orbit interactions Victor Galitski The spectrum of many electronic systems contains band degeneracies, which can be thought of as monopoles in momentum space leading to a non-trivial topological structure of the Fermi surface. This structure is characterized by two quantities: curvature and metric, which, being gauge invariant, are in principle observable in experiment. In electronic systems with spin-orbit interactions, the Berry's curvature determines the so-called spin Hall conductivity, which may be related to observable spin accumulation near the edges. We consider Rashba, Dresselhaus, and Luttinger models and study the effect of interactions on the topology of the Fermi surface in these systems. We find that interactions renormalize the spin-orbit couplings but in certain cases do not change the Berry's phase structure. This suggests that the non-trivial geometry of the Fermi surface is a true Fermi liquid property. [Preview Abstract] |
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