Bulletin of the American Physical Society
2009 APS March Meeting
Volume 54, Number 1
Monday–Friday, March 16–20, 2009; Pittsburgh, Pennsylvania
Session D22: Focus Session: Spins in Group IV Semiconductors |
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Sponsoring Units: GMAG DMP FIAP Chair: Bruce Kane, LPS, University of Maryland Room: 324 |
Monday, March 16, 2009 2:30PM - 3:06PM |
D22.00001: Quantum control of donor electron charge and spin in Si close to a Si-SiO$_2$ interface Invited Speaker: Doped Si is a promising candidate for quantum information processing due to its potential for scalability, long spin coherence times, and the continuing progress on Si material processing, technology and miniaturization over several decades. I will discuss important issues for single- and two- qubit operations in Si-based quantum computer proposals involving P donors close to a SiO$_2$ interface. For a single donor, donor-bound electron manipulation between the donor and the interface by electric and magnetic fields is investigated [1,2]. Valley interference and how it affects a donor electron close to an interface under an applied electric field is also considered, taking the valley-orbit coupling at the interface as a parameter. It will be shown that, for nonzero interface valley-orbit coupling, this configuration leads to oscillatory behavior of the donor ionization time as a function of the donor-interface distance while the characteristic ionization field does not oscillate with distance [3]. The physical origin of these effects, and their impact in proposed operations of donor-based qubits, will be discussed. For a donor pair, the exchange coupling of interface electrons bound to the donors double well potential is calculated within the Heitler London approach [2,4]. The feasibility and convenience of performing exchange operations for electron pairs at the interface as opposed to around the donors will be assessed. Work done in collaboration with M.J.Calderon and S. Das Sarma and partially supported by LPS-NSA and MICINN-Spain. \\[4pt] [1] M.J. Calderon, B. Koiller, X. Hu, and S. Das Sarma, Phys. Rev. Lett. 96, 096802 (2006).\\[0pt] [2] M.J. Calderon, B. Koiller and S. Das Sarma, Phys. Rev. B 75, 125311 (2007).\\[0pt] [3] M.J. Calderon, B. Koiller and S. Das Sarma, Phys. Rev. B 77, 155302 (2008).\\[0pt] [4] A. L. Saraiva, M. J. Calderon, and B. Koiller Phys. Rev. B 76, 233302 (2007). [Preview Abstract] |
Monday, March 16, 2009 3:06PM - 3:18PM |
D22.00002: A new electrical readout mechanism for Si:P qubits Dane R. McCamey, G.W. Morley, S.-Y. Paik, S.-Y. Lee, L.-C. Brunel, J. van Tol, C. Boehme Phosphorus donor spins in silicon are a promising candidate for the implementation of quantum bits, and electrical detection is viewed as the most promising route towards the single donor readout required to further advance such concepts. We will discuss a major limitation to commonly used electrical detection schemes. The standard way to electrically detect Si:P spin states involves utilizing spin dependent recombination with nearby probe spins, usually of defects at the Si-SiO$_2$ interface. This process has a fast, fixed timescale, thereby limiting coherence times. We find that these times are of order $1 \mu$s, in agreement with other studies. By moving to high magnetic fields ($B > 8$ T) we enter a new regime - complete electron polarization. This allows us to utilize a different readout mechanism, namely, capture into the donor D$^-$ state which causes a decrease in the photocurrent in the sample. We have developed a system which allows us to investigate the donor spin phase coherence times at these high magnetic fields; we find them to be over $100 \mu$s [1]. Additionally, the signal observed at these high fields is significantly larger ($\Delta I/I \sim 5$ \%) than at low fields, providing a pathway towards single spin detection. [1] PRL \textbf{101}, 207602 (2008) [Preview Abstract] |
Monday, March 16, 2009 3:18PM - 3:30PM |
D22.00003: SU(4) Kondo in a single donor transport in a Si FinFET G.P. Lansbergen, G.C. Tettamanzi, A. Verduijn, M. Blaauboer, S. Rogge Recently, single dopants became experimentally accessible and there is a large effort to exploit their atomic characteristics in nano devices. Orbital Kondo effects in Si and SiGe are of fundamental interest since they explore the role of the valley degree of freedom in this material system. It has been theoretically predicted that the valley degeneracy leads to SU(4)-correlations which entangles the spin and momentum of exchanged electrons. Here, we experimentally study Kondo effects in a novel system, a single shallow donor in a three-terminal geometry. We use Si wrap-around gate (FinFET) devices with a single Arsenic donor atom in the channel dominating the sub-threshold transport characteristics. The ground state of this system originates from the hybridization of the donor hydrogen-like state which has no valley degeneracy (due to the strong valley-orbit interaction) and a quantum dot-like state which is two-fold valley degenerate. In the Coulomb-blockade regime with a single electron on the system we observe a set of transport resonances. We show these resonances to originate from Valley Kondo effects by means of their dependence on temperature, magnetic field, orbital splitting and their substructure. The entanglement between spin and momentum provides new opportunities for spin control in silicon. For example, we show that this device operates as a gated spin filter in Si with a potentially high transitivity. [Preview Abstract] |
Monday, March 16, 2009 3:30PM - 3:42PM |
D22.00004: Electric field control of spins in a silicon two-dimensional electron gas. R. Jansen, B.C. Min, S. P. Dash, R. S. Patel, M. P. de Jong A key objective in the development of semiconductor spintronics is the active control of spins in semiconductors. The manipulation by electric rather than magnetic fields is preferred as this is more efficient for nanoscale high frequency devices. Proposals for electric spin control, for example for use in a spin transistor, have so far focused on mechanisms that require spin-orbit interaction. Unfortunately, in silicon, the mainstream semiconductor, the weak spin-orbit interaction renders these mechanisms unsuited. Hence, alternative approaches are paramount to the success of semiconductor spintronics. Here we demonstrate spin control by electric fields in a silicon two-dimensional electron gas (2DEG), exploiting the discrete electronic structure of the 2DEG. This, in combination with an electric field, allows spin manipulation without the need for spin-orbit interaction. The spin control is manifested as resonances in the tunnel magnetoresistance between the Si 2DEG and a ferromagnetic tunnel contact, with amplitude of up to 8{\%}. [Preview Abstract] |
Monday, March 16, 2009 3:42PM - 3:54PM |
D22.00005: Injection and extraction of spins in a Silicon lateral transport structure Olaf van 't Erve, Chaffra Awo-Affouda, Aubrey Hanbicki, Michael Holub, Connie Li, Phillip Thompson, Berend Jonker Significant progress has recently been made on spin injection into the technologically important semiconductor, Si. A nonlocal measurement technique, which excludes spurious contributions from AMR and local Hall effects, was used to show lateral diffusive spin transport through silicon using Fe/Al2O3 surface contacts. The tunnel contacts are used to create and analyze the flow of pure spin current in a silicon transport channel. The nonlocal signal shows that a spin current can be electrically detected after diffusive transport through the silicon transport channel and the signal depends on the relative orientation of the magnetization of the injecting and detecting contacts. Hanle effect measurements up to 125 K demonstrate that the spin current can be modulated by a perpendicular magnetic field, which causes the electron spin to precess and dephase in the channel during transport. By changing the bias on the injector contact we can either inject or extract spin from the Silicon channel. Here we will show using Hanle and lateral spin- valve measurements that we can change the polarization of the spin accumulation by going from the injection regime to the extraction regime and we will compare the efficiency of spin- injection versus spin extraction. [Preview Abstract] |
Monday, March 16, 2009 3:54PM - 4:06PM |
D22.00006: Spin Precession in Oblique Magnetic Fields Jing Li, Biqin Huang, Ian Appelbaum Spin precession and dephasing (``Hanle effect'') provide an unambiguous means to establish the presence of spin transport in semiconductors. We compare theoretical modeling with experimental data from drift-dominated silicon spin-transport devices, illustrating the non-trivial consequences of employing oblique magnetic fields (due to misalignment or intentional, fixed in-plane field components) to measure the effects of spin precession. Model results are also calculated for Hanle measurements under conditions of diffusion-dominated transport, revealing an expected Hanle peak-widening effect induced by the presence of fixed in-plane magnetic bias fields. [Preview Abstract] |
Monday, March 16, 2009 4:06PM - 4:18PM |
D22.00007: Geometric dephasing-limited Hanle effect in long-distance lateral silicon spin transport devices Biqin Huang, Hyuk-Jae Jang, Ian Appelbaum Using ballistic injection and hot-electron spin filter detection, lateral spin transport over 2 millimeters is demonstrated in undoped single-crystal Silicon. In these devices, geometrically-induced dephasing (Hanle effect) is so strong that the effects of spin precession could not be measured with only a single-axis magnetic field. However, a two-axis magnetic field can be used to obtain unequivocal evidence of spin precession and transport despite full dephasing. We therefore conclude that there is never a reason to avoid measurement of spin precession as unequivocal evidence of spin transport in semiconductor devices. [Preview Abstract] |
Monday, March 16, 2009 4:18PM - 4:30PM |
D22.00008: Non-ohmic spin transport in n-type doped silicon H.-Jae Jang, Jing Xu, Jing Li, Biqin Huang, Ian Appelbaum In contrast with undoped silicon transport layers [1], conduction-band bending in n-type doped silicon spintronic devices results in non-ohmic spin-polarized electron transport [2]: for low applied voltage drops across the transport layer, a potential well causes confinement of electrons in the silicon transport layer, and they must diffuse against an electric field to escape. Numerical simulation using a Monte Carlo algorithm reveals that the average transit time across our 3.3 um Si layer can be changed over 4 orders of magnitude by varying an applied voltage. We can therefore deduce a long spin lifetime [3] in n-type doped silicon from comparison between experimental data and fitting-parameter-free simulation results in spite of the short transport distance. References [1] Ian Appelbaum et al. Nature 447, 295 (2007). [2] H.-Jae. Jang et al. Phys. Rev. B 78, 165329 (2008). [3] Biqin Huang et al. Phys. Rev. Lett. 99, 177209 (2007). [Preview Abstract] |
Monday, March 16, 2009 4:30PM - 4:42PM |
D22.00009: Indirect Optical Injection of Carriers and Spin in Silicon JinLuo Cheng, Julien Rioux, John Sipe Degenerate two-photon indirect absorption in silicon is an important limiting effect on the use of silicon structures for all-optical information processing at telecommunication wavelengths. Optical injection of spins in silicon is potentially important for spintronics applications. We theoretically investigate one- and two-photon indirect absorption in silicon, using a pseudopotential description of energy band and the adiabatic bond charge model to describe phonon dispersion and polarization. Spin injection is calculated as well. We compare our results with experiments. [Preview Abstract] |
Monday, March 16, 2009 4:42PM - 4:54PM |
D22.00010: Transient Current Spectroscopy of a Si Quantum Dot Ming Xiao, Hongwen Jiang We present a transient current spectroscopy study of a Si-MOS based quantum dot. The study was conducted in the few electron region. A voltage pulse pumped the electrons into an excited orbital state and the non-equilibrium transient current through the dot was recorded. The evolution of the excited state as a function of magnetic field shows signatures of a transition from a spin singlet state to a triplet state of an electron pair. A pump-and-probe technique was employed to set a lower limit of the triplet-singlet relaxation time. The work was sponsored by United States Department of Defense. [Preview Abstract] |
Monday, March 16, 2009 4:54PM - 5:06PM |
D22.00011: Magneto-transport properties of Si-based Nanowires Sungmu Kang, Jugdersuren Battogtokh, Andrew C. Buchele, David A. McKweon, Ian L. Pegg, John Philip We report the growth and magneto-transport properties of Si-based, Mn$_{5}$SiC nanowires grown using chemical vapor deposition. High resolution transmission electron microscopy and x-ray diffraction studies show that the nanowires crystallize in Mn$_{5}$SiC orthorhombic structure. Ferromagnetic Mn$_{5}$SiC nanowires were grown using a coordination complex-based precursor. In the presence of an external magnetic field, Mn$_{5}$SiC nanowire-based devices exhibit spin dependent transport properties at room temperature. A large change in current with almost two orders of magnitude increase is observed when a small field is applied parallel to the axial direction of the nanowire. We will discuss in details the magneto-transport properties of Mn$_{5}$SiC nanowire based devices. [Preview Abstract] |
Monday, March 16, 2009 5:06PM - 5:18PM |
D22.00012: Prospects of Spin Injection in Germanium Nanowires En-Shao Liu, Kamran Varahramyan, Junghyo Nah, Sanjay Banerjee, Emanuel Tutuc Efficient spin injection from ferromagnetic (FM) contacts into semiconductors (SC), the prerequisite for spin-based semiconductor devices, is typically suppressed by the conductivity mismatch between the FM contact and the SC. A significant spin injection can be achieved however if the contact resistivity at the FM/SC interface is appropriately engineered [1]. We report here contact resistivity measurements of n-type germanium (Ge) nanowires (NWs) with two FM metals, namely permalloy (Ni$_{80}$Fe$_{20})$ and nickel (Ni), for NW doping densities between 10$^{16}$ and 10$^{20 }$cm$^{-3}$, and for temperatures between 77K to 300K. Using back-gated two- and four-terminal measurements, we show that the contact resistivity varies from 10$^{-7 }(\Omega $ cm$^{2})$ for highly-doped NWs, to 10$^{-4 }(\Omega $ cm$^{2})$ for moderately-doped NWs. Within the framework of the spin injection theory [1], these values indicate that by optimizing the device parameters, namely the choice of FM metal, contact width, NW diameter and doping density, spin injection into Ge NWs is possible. [1] A. Fert and H. Jaffres, Phys. Rev. B. \textbf{64}, 184420 (2001) [Preview Abstract] |
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