Bulletin of the American Physical Society
APS March Meeting 2011
Volume 56, Number 1
Monday–Friday, March 21–25, 2011; Dallas, Texas
Session D8: Spin Currents |
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Sponsoring Units: GMAG Chair: Supriyo Datta, Purdue University Room: Ballroom C4 |
Monday, March 21, 2011 2:30PM - 3:06PM |
D8.00001: Spin Currents in Silicon Invited Speaker: I will discuss the results of our recent spin injection experiments using long-distance non-degenerate undoped (and n-type doped) Si devices. We have a unique capability to recover the details of electron transport on a sub-ns timescale through a ``Larmor clock'' transformation of spin precession data, despite using only quasistatic current measurements. I suggest that this is potentially a new tool for probing non-equilibrium phenomena in semiconductors, revealing both intrinsic and extrinsic materials properties through sensitivity to subtleties of the bandstructure and impurity spectrum. [Preview Abstract] |
Monday, March 21, 2011 3:06PM - 3:42PM |
D8.00002: Spin Hall Effects in Ferromagnet-Semiconductor Heterostructures Invited Speaker: The effect of spin-orbit coupling on charge transport has long been studied in the form of the anomalous Hall effect in ferromagnets. Charge current in a ferromagnetic channel is intrinsically spin polarized, and asymmetric transverse scattering of spin-up and spin-down electrons due to spin-orbit coupling leads to charge accumulation on the channel edges. Recent breakthroughs in the ability to inject and detect non-equilibrium spin populations in non-ferromagnetic materials have opened up new avenues to study related phenomena. Of particular interest is the spin Hall effect (SHE) in which an ordinary charge current induces a transverse spin current. The resultant spin accumulation at the channel edges was first detected optically [Y. K. Kato \textit{et al.}, Science 306, 1910 (2004) ; J. Wunderlich\textit{ et al.}, Phys. Rev. Lett. 94, 047204 (2005)]. We report on an all-electrical measurement of the SHE in Fe/$n$-In$_{x}$Ga$_{1-x}$As heterostructures. The edge spin accumulation is detected with spin-sensitive Fe/Schottky tunnel barrier contacts. We investigate the bias and temperature dependence of the SHE and successfully determine the skew and side-jump contributions [E. S. Garlid\textit{ et al.}, Phys. Rev. Lett. 105, 156602 (2010)]. Additionally, we have studied the inverse spin Hall effect (iSHE), in Fe/$n$-GaAs devices. Spin current injected into $n$-GaAs by a biased Fe/Schottky contact results in a spin-dependent Hall voltage. The iSHE signal is an order of magnitude larger than that expected from SHE measurements in the same heterostructure. Temperature dependence, nuclear magnetic resonance, and field cycling measurements show conclusively that the iSHE is coupled to the dynamically polarized nuclear spins. We have therefore discovered a new contribution to spin Hall effects: the hyperfine coupling. Work done in collaboration with E.S. Garlid, Q.O. Hu, C.J. Palmstr{\o}m, and P.A. Crowell. Funding provided by NSF DMR 0804244, ONR MURI, and NSF MRSEC and NNIN programs. [Preview Abstract] |
Monday, March 21, 2011 3:42PM - 4:18PM |
D8.00003: Electrostatically Manipulated Ballistic Spin Currents Invited Speaker: Two decades ago Datta and Das published a remarkable paper [1] concerning spin polarized ballistic electron currents in a semiconductor channel and the Rashba spin orbit interaction. They predicted that the source-drain conductance of a spin-injected Field Effect Transistor (spin FET) would oscillate periodically as a function of monotonically increasing gate voltage. We have observed Datta Das oscillations using spin-FETs with ferromagnetic metal electrodes as source and drain [2]. The channel is composed of a high mobility InAs single quantum well heterostructure with strong spin-orbit interaction. The source-drain length is less than the electron mean free path at T=1.8 K. Using the nonlocal geometry, diffusive carriers are removed at a remote ground and the channel conductance is dominated by a current of spin polarized ballistic electrons. A conductance that oscillates as a function of gate voltage is observed. The oscillation amplitude is calibrated from the lateral spin valve magnetoresistance. The spin-orbit interaction parameter is determined from beats in Shubnikov-de Haas data. Thus, the fit to theory has no adjustable parameters other than a small phase factor. Finally, we compare the temperature dependence of the oscillation amplitude with that of the carrier mean free path. The importance to Spintronics, which proposes the use of both spin and charge as state variables, is the demonstration that carrier spin orientation can be modulated by voltage, a parameter normally associated with charge. \\[4pt] [1] S. Datta and B. Das, Appl. Phys. Lett. v. 56, 665 (1990). \\[0pt] [2] H.C. Koo, J.H. Kwon, J. Eom, J. Chang, S.H. Han and M. Johnson, Science v. 35, 1515 (2009). [Preview Abstract] |
Monday, March 21, 2011 4:18PM - 4:54PM |
D8.00004: Logic Devices Based on Spin Current Invited Speaker: The need to find low power alternatives to digital electronics circuits has led to increasing interest in alternative switching schemes like the magnetic quantum cellular automata that store information in nanomagnets which communicate through their magnetic fields. A recent proposal called all spin logic (ASL) proposes to communicate between nanomagnets using spin currents which are spatially localized and can be conveniently routed. In this talk we present a model for ASL devices that is based on established physics and is benchmarked against available experimental data. We investigate switching energy- delay of ASL devices and provide frameworks that allow simple comparisons with charge based devices like CMOS and can help to determine possible use of ASL in future logic implementation. Expected scaling of switching energy-delay of ASL devices as magnets are downscaled while retaining their stability against thermal fluctuations will be presented. [Preview Abstract] |
Monday, March 21, 2011 4:54PM - 5:30PM |
D8.00005: Optical detection of spin currents Invited Speaker: Extensive efforts are currently being devoted to developing spintronics. Several techniques have been developed to generate pure spin currents in many materials and structures. However, there is still no method available that can be used to directly detect pure spin currents, which carry no net charge current and no net magnetization. Currently, studies of pure spin currents rely on measuring the induced spin accumulation with optical techniques or spin-valve configurations. I will discuss observation of a second-order nonlinear optical effect of pure spin currents that can be used for the non-invasive, non- destructive, and real-time imaging of pure spin currents. This effect is caused by a subtle imbalance of the Faraday rotation of electrons with opposite spin orientations [1]. In our experiment, a transient pure spin current was injected in a GaAs crystal by a quantum interference and control technique using a pair of phase-locked ultrafast laser pulses. Second- harmonic generation of an ultrafast probe pulse with a central wavelength of 1760 nm was observed [2]. We systematically studied the second-harmonic power as a function of the probe delay, probe position, spin current density, and carrier density. All the observations are consistent with a second- order nonlinear optical effect induced by the pure spin current. Since this effect does not rely on optical resonances, it can be used to detect pure spin currents in a wide range of materials with different bandstructures. Furthermore, the control of nonlinear optical properties of materials with pure spin currents may have potential applications in photonics integrated with spintronics. \\[4pt] [1] J. Wang, B. F. Zhu, and R. B. Liu, Phys. Rev. Lett. 104, 256601 (2010).\\[0pt] [2] L. K. Werake and H. Zhao, Nat. Phys. 6, 875 (2010). [Preview Abstract] |
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