Bulletin of the American Physical Society
APS March Meeting 2015
Volume 60, Number 1
Monday–Friday, March 2–6, 2015; San Antonio, Texas
Session Q31: Focus Session: Spin-Dependent Phenomena in Semiconductors: Spin Injection |
Hide Abstracts |
Sponsoring Units: GMAG DMP FIAP Chair: Connie Li, Naval Research Laboratory Room: 207A |
Wednesday, March 4, 2015 2:30PM - 3:06PM |
Q31.00001: Spin-dependent transport across SrTiO$_{3}$-based heterostructures Invited Speaker: Adrian Swartz Identification of candidate spin-preserving materials is of crucial importance for the realization of functional spin logic devices. An oxide spin channel is particularly attractive because of the ease of epitaxial integration with other functional complex oxides, which could manipulate spins in transit. Electron-doped SrTiO$_{3}$ is one emerging material where high mobility conduction has been realized at the interface between LaAlO$_{3}$ and SrTiO$_{3}$, as well as in more traditional semiconducting Nb-doped SrTiO$_{3}$ thin films. We have investigated spin injection in both systems using a three-terminal (3T) geometry with ferromagnetic electrodes and have observed magnetoresistance commonly attributed to dephasing of an ensemble spin population (Hanle effect), with associated spin lifetimes in the range of 40-130 ps, large enough for the realization of lateral spin transport devices. However, such a picture fails to explain all the experimentally observed behavior. Further experiments indicate contributions from magnetic-field modulation of spin-dependent transport through defect states in the barrier region, suggesting that the 3T approach does not uniquely probe spin accumulation in the SrTiO$_{3}$ channel. [Preview Abstract] |
Wednesday, March 4, 2015 3:06PM - 3:18PM |
Q31.00002: Spin Transport Properties in Nondegenerate Si at Room Temperature Takayuki Tahara, Hayato Koike, Tomoyuki Sasaki, Yuichiro Ando, Makoto Kameno, Yoshishige Suzuki, Masashi Shiraishi So-called beyond-CMOS technologies have been intensively investigated. Among them, Si spintronics is now a promising candidate, since Si has good spin coherence, enabling novel spin-based logic systems. We have been investigating spin transport properties in degenerate Si up to room temperature (RT)),\footnote{T. Suzuki, T. Sasaki, M. Shiraishi et al., Appl. Phys. Exp. 4, 023003 (2011)} and recently, spin transport in a non-degenerate n-Si at RT was successfully achieved,\footnote{T. Sasaki, T. Tahara, M. Shiraishi et al., Phys. Rev. Applied, 2, 034005 (2014).} where the doping concentration of Si was $2\times10^{18}$ cm$^{-3}$. Spin drift in non-degenerate Si allows apparent modulation of Hanle spin signals under applications of bias- and gate-electric fields.\footnote{Sasaki, Phys. Rev. Applied, 2, 034005 (2014).} The magnitude of the spin signals exceeds 1 mV under an bias electric current of 1 mA, which is ten times greater than previously reported values\footnote{T. Sasaki, M. Shiraishi et al., Appl. Phys. Lett. 104, 052404 (2014).} in degenerate-Si-based spin transport devices. The detail of the observation of large spin signals and other spin transport properties will be discussed in the presentation. [Preview Abstract] |
Wednesday, March 4, 2015 3:18PM - 3:30PM |
Q31.00003: Investigation of spin drift velocity and the modulation of spin signals under spin drift in highly-doped n-type Si Makoto Kameno, Yuichiro Ando, Teruya Shinjo, Masashi Shiraishi, Hayato Koike, Tomoyuki Sasaki, Tohru Oikawa, Toshio Suzuki Spin drift enables to modulate a spin transport length scale in semiconductor.\footnote{Z.G. Yu and M.E. Flatte, Phys. Rev. B 66, 201202(R) (2002).} We have experimentally investigated a role of spin drift in spin transport in highly-doped n-Si, i.e., the modulation of a spin transport length scale by using an electrical spin transport method.\footnote{M. Kameno et al., Appl. Phys. Lett. 101, 122413 (2012).} The results directly show that spin drift becomes prominent in spin transport in semiconductor. In addition, spin drift velocity in the highly-doped Si channel was quantitatively estimated by introducing a new experimental technique.\footnote{M. Kameno et al., Appl. Phys. Lett. 104, 092409 (2014).} It was revealed that Hanle-type spin precession signals from the Si were modulated by spin drift and were theoretically reproduced. [Preview Abstract] |
Wednesday, March 4, 2015 3:30PM - 3:42PM |
Q31.00004: Spin lifetime dependence on spin injection orientation in strained silicon films Joydeep Ghosh, Dmitri Osintsev, Viktor Sverdlov, Siegfried Selberherr Growing technological challenges and costs are guiding MOSFET scaling to an end. This accelerates the search of alternative devices principles, including concepts based on electron spin. As of the ongoing shift to thin silicon films and fins-based devices for the 14nm node and beyond, spin lifetime in such structures becomes a dominant issue. Large spin lifetime enhancement in (001) thin silicon films subjected to [110] uniaxial tensile stress was predicted for spin injected perpendicular to the film [1]. Here we find that the spin relaxation rate is further reduced and the spin lifetime is thus increased for spin injected in-plane. To explain the observed behavior we look at the spin relaxation hot spots. For an in-plane injection along OX the spin expectation value projections at the hot spots are: $\sigma_x=\sin^2(\arctan(p_x/p_y)),\sigma_y=-(p_y/p_x)\sigma_x,\sigma_z=$0, while for spin injected perpendicular to the film the spin expectation value at the hot spots is zero, resulting in maximal spin randomization at any in-plane momentum ($p_x,p_y$). Therefore the spin relaxation rate is the strongest for spin injected perpendicularly explaining the spin relaxation time increase for an in-plane spin injection. 1.D.Osintsev {\it et al., Solid-State Electron.}{\bf 90}, 34 (2013). [Preview Abstract] |
Wednesday, March 4, 2015 3:42PM - 3:54PM |
Q31.00005: Challenging the spin accumulation interpretation of local ``3T" measurements Holly Tinkey, Ian Appelbaum, Pengke Li The recent observation of magnetoresistance in local ``three-terminal" (3T) measurements on ferromagnet/ insulator/ semiconductor junctions have spawned many claims of direct bulk spin injection or ``accumulation". We present a self-consistent model to rigorously calculate expected voltage changes due to electrochemical potential splitting from spin accumulation driven by pure elastic tunnel injection in such junctions, and find that the experimentally observed magnetoresistance vastly exceeds theoretical predictions in all doping, temperature, and bias voltage regimes. Our own experimental measurements using inelastic electron tunneling spectroscopy reveal that extrinsic impurities and defects within the junctions are responsible for the observed magnetoresistance signals, which cannot possibly be attributed to spin dephasing of polarized bulk electrons from elastic injection as claimed by proponents of the method. [Preview Abstract] |
Wednesday, March 4, 2015 3:54PM - 4:06PM |
Q31.00006: Exchange Driven Spin Relaxation in Ferromagnet/Oxide/Semiconductor Heterostructures Yu-Sheng Ou, Yi-Hsin Chiu, Nicholas Harmon, Patrick Odenthal, Roland Kawakami, Michael Flatt\'e, Ezekiel Johnston-Halperin Time-resolved Kerr rotation (TRKR) is employed to study the exchange coupling between spin ensembles in GaAs and a neighboring ferromagnet (FM) in an Fe/MgO/GaAs heterostructure. The time-resolved spin dynamics in GaAs provide local magnetometry, revealing the strength and sign of the exchange field as well as its impact on electron and nuclear spins. Consistent with previous studies, we see a hyperpolarization of the nuclei induced by the dynamic exchange at the Fe/MgO/GaAs interface that results in a large effective nuclear field on the electrons (Bn = 0.2 T). Unexpectedly, we observe that the spin relaxation time in GaAs, T2*, depends on the strength of the exchange-driven nuclear field rather than the applied field. In addition, the temperature dependence of T2* shows a crossover of relaxation mechanism from hyperfine dominated to D'yakonov-Perel' (DP) dominated at temperatures above 40 K. These results not only resolve a long-lasting puzzle of the GaAs spin relaxation mechanism, but further demonstrate the ability to detect exchange-driven dissipation in FM/NM heterostructures. We discuss the potential for this work to define a novel detection scheme for exchange-driven spin injection in FM/semiconductor heterostructures, such as ferromagnetic resonance driven spin pumping. [Preview Abstract] |
Wednesday, March 4, 2015 4:06PM - 4:18PM |
Q31.00007: Non-local spin transport with two coupled channels: Manifestation of the inter-channel tunneling in the shapes of the Hanle curves Mikhail Raikh, Robert Rouny, Magan Prestgard, Ashutosh Tiwari, Eugene Mishchenko Dynamics of charge-density fluctuations in a system of two tunnel-coupled channels contains two diffusion modes with dispersion $i\omega=Dq^2$ and $i\omega =Dq^2+\frac{2}{\tau_t}$, where $D$ is the diffusion coefficient and $\tau_t$ is the tunneling time between the channels. The dispersion of corresponding spin-density modes depends on magnetic field as a result of spin precession with Larmour frequency, $\omega_L$. The presence of two modes affects the shape of the Hanle curve, describing the non-local resistance between the injector and the detector. We calculate the shapes, $R_{11}(\omega_L)$ and $R_{12}(\omega_L)$, of the Hanle curves, for geometries in which detector is located, respectively, in the same and in the different channel than the detector. We demonstrate that the relative shapes of $R_{11}(\omega_L)$ and $R_{12}(\omega_L)$ depend on the ratio $\tau_t/\tau_s$, where $\tau_s$ is the spin-diffusion time. If the coupling between the channels is local, i.e. only at the point $x=0$, then the difference of the shapes of $R_{11}(\omega_L)$ and $R_{12}(\omega_L)$ curves reflects the difference in statistics of diffusive trajectories which ``switch" or do not switch near $x=0$. [Preview Abstract] |
Wednesday, March 4, 2015 4:18PM - 4:30PM |
Q31.00008: Detecting spin accumulation in FM/$n$-GaAs heterostructures using ferromagnetic resonance Changjiang Liu, Chad Geppert, Kevin Christie, Gordon Stecklein, Sahil Patel, Chris Palmstr{\O}m, Paul Crowell A distinguishing feature of spin accumulation in ferromagnet (FM)/semiconductor heterostructures is precession. This is the basis for detection techniques such as the Hanle effect, but these approaches become less effective as the spin lifetime in the semiconductor decreases. We report here on a technique in which the source magnetization is forced to precess at the ferromagnetic resonance frequency, allowing for the detection of spin accumulation even when the spin lifetime is short (less than 100 psec). The samples used in the experiments are MBE-grown FM/(001) $n$-GaAs heterostructures, in which the FM are the Heusler alloys Co$_{2}$MnSi and Co$_{2}$FeSi. These samples show non-local spin valve and Hanle signals in conventional electrical spin injection/detection measurements at low temperatures. Using the FMR technique, we detect the spin accumulation from 30 K to room temperature as a sharp resonance peak. The frequency dependence of the magnitude of the resonance peak allows for a measurement of the spin lifetime. Spin lifetimes as short as 40 psec are measured at room temperature in channels doped at 3x10$^{16\, }$cm$^{-3}$. [Preview Abstract] |
Wednesday, March 4, 2015 4:30PM - 4:42PM |
Q31.00009: Spin transport at high temperatures in epitaxial Heusler alloy/n-GaAs lateral spin valves Timothy A. Peterson, Kevin D. Christie, Sahil J. Patel, Paul A. Crowell, Chris J. Palmstr{\O}m We report on electrical injection and detection of spin accumulation in ferromagnet/$n$-GaAs lateral spin-valve devices, observed up to and above room temperature. The ferromagnet in these measurements is the Heusler alloy Co$_{\mathrm{2}}$FeSi, and the semiconductor channel is GaAs doped at $3 \times10^{16}$ cm$^{-3}$. The spin signal is enhanced by operating the detection contact under forward bias. The enhancement originates from drift effects at low-temperatures and an increase of the detection efficiency at all temperatures. The detector bias dependence of the observed spin-valve signal is interpreted by taking into account the quantum well (QW) which forms in the degenerately doped region immediately behind the Schottky tunnel barrier. In particular, we believe the QW is responsible for the minority spin accumulation (majority spin current) under large forward bias. The spin diffusion length and lifetime are determined by measuring the separation dependence of the non-local spin valve signal in a family of devices patterned by electron beam lithography. A spin diffusion length of 700 nm and lifetime of 46 picoseconds are found at a temperature of 295 K. [Preview Abstract] |
Wednesday, March 4, 2015 4:42PM - 4:54PM |
Q31.00010: g-factor modification by an in-plane electric field in a bulk In$_{0.03}$Ga$_{0.97}$As epilayer Marta Luengo-Kovac, Simon Huang, Rachel Goldman, Vanessa Sih The response of an electron spin to a magnetic field, determined by the g-factor, is important for any spin-based device. The modification of the g-factor by a perpendicular electric field has been demonstrated in quantum wells and dots. This can be explained by the electric field shifting the electron wavefunction into the barrier. We found that the g-factor also changes when an in-plane electric field is applied across an In$_{0.03}$Ga$_{0.97}$As epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to measure the g-factor independently of the spin-orbit fields. Measurements performed along the [110] and [1-10] crystal axes show the same electric-field dependence of the g-factor, indicating that this change in the g-factor is not related to the spin-orbit fields. Temperature and voltage dependent photoluminescence measurements were also performed, showing that change in the g-factor was not caused by channel heating by the electric field. As there is no quantum confinement along the direction of the electric field, this change in the g-factor is fundamentally different from that seen in quantum wells and dots. [Preview Abstract] |
Wednesday, March 4, 2015 4:54PM - 5:06PM |
Q31.00011: Spin Lifetimes in annealed GaInNAs epilayers Yutsung Tsai, Biplob Barman, Thomas Scrace, Athos Petrou, Miwa Fukuda, Ian Sellers, Mathieu Leroux, Mohamed Khalfioui We have carried out Hanle measurements of the electron spin lifetime $T_{S} $in optically pumped annealed GaInNAs epilayers (undoped and p-type doped). The samples were placed in a 7T optical magnet cryostat with the magnetic field applied in the epilayer plane. The emitted light was collected along the normal to the epilayers. The PL was excited using the 1064 nm line from a Nd:YAG laser which gives a polarization P $=$ 5{\%} at B$=$0. The transverse magnetic field results in a reduction of $P$, from which we determine $T_{S}$. At $T=$50 K, the electron spin lifetime $T_{S} $was measured to be 15 ps. As the sample temperature increases, $T_{S} $decreases ($T_{S\thinspace }=$ 7 ps at T $=$ 150 K). Our Hanle results are in agreement with the $T_{S} $values measured by Lombez \textit{et al}. using time-resolved photoluminescence spectroscopy [2]. The observed sharp reduction in $T_{S} $in annealed samples is interpreted as due to the D'yakonov-Perel' spin relaxation mechanism. [3] In annealed samples the momentum relaxation time increases, resulting in a reduction of $T_{S}$ [2] L. Lombez et al, Appl Phys Lett 87, 252115(2005) [3] M.I. D'yakonov and V.I. Perel', Soviet Physics JETP, 33, 1053(1971) [Preview Abstract] |
Wednesday, March 4, 2015 5:06PM - 5:18PM |
Q31.00012: Interfacial Structure in Co$_{2}$MnSi/GaAs(001) Spin Injection Heterostructures Sahil Patel, Kevin Christie, Chad Geppert, Gordon Stecklein, Lee Wienkes, Fengyuan Shi, Ashutosh Rath, Brian Schultz, Oleg Mryasov, William Butler, Paul Voyles, Paul Crowell, Christopher Palmstrom We report on the role of the interface formation and structure of molecular beam epitaxially grown Co$_{2}$MnSi/GaAs(001) heterostructures with measured spin accumulations of approximately 60{\%} at 30K in GaAs. \textit{In-situ} scanning tunneling microscopy (STM) was used to study morphology and x-ray photoelectron spectroscopy (XPS) for the evolution of core level emission peaks as a function of film thickness for thin epitaxial Co$_{2}$MnSi films. Alternate monolayers of Co and MnSi were deposited to form an epitaxial template layer upon which codeposition of Co, Mn, and Si was used to grow thicker single crystal films. By combining the in-situ XPS elemental layer-by-layer peak evolutions and STM results with ex-situ high angular dark field scanning transmission electron microscopy (HAADF-STEM), x-ray diffraction, SQUID magnetometry and first-principles calculations, consistent models of the growth and interface formation have been developed and will be presented. This work was supported by C-SPIN, one of the six centers of STARnet, a SRC program sponsored by MARCO and DARPA; and by the NSF MRSEC program. [Preview Abstract] |
Wednesday, March 4, 2015 5:18PM - 5:30PM |
Q31.00013: Revisiting the measurement of the spin relaxation time in graphene-based spintronic devices Hiroshi Idzuchi, Albert Fert, YoshiChika Otani Spin transport in graphene has strongly drawn attention because of the expected long spin relaxation time $\tau $sf, but, $\tau $sf derived from experiments is rarely above 1 ns, shorter than theoretically expected and also largely dispersed [1]. Here we reanalyze Hanle curves in graphene-based lateral spin valves with various contacts by using the recently established model of Hanle effect taking into account the spin absorption by contacts [2]. We found the reanalysis of Hanle curves of four samples from transparent contacts to tunnel contacts, reported in ref.3, gives longer and much less dispersed $\tau $sf ranging around 500 ps compared to the original values ranging from 84 ps to 495 ps. Extending our analysis to typical recent experiments with long spin diffusion length, $\lambda \sim $10 $\mu $m, we find the spin absorption is even more pronounced because the contact resistance R needed to suppress the spin absorption scales with the spin resistance $\propto \quad \lambda $. Thus R in the range of 100 kOhm is generally not large enough to suppress the spin absorption, and taking into account the contacts is more important to characterize the real $\tau $sf in graphene with $\lambda $ in this range. \\[4pt] [1] D. Pesin and A. H. MacDonald, Nmat 11, 409 (2012). [2] H. Idzuchi et al., PRB 89, 081308(R) (2014). [3] W. Han et al., PRL 105, 167202 (2010). [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