Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session F42: Spin Transport in Quantum Dots and NanowiresFocus
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Sponsoring Units: GMAG DMP DCOMP FIAP Chair: Bernhard Urbaszek, CNRS Toulouse Room: 389 |
Tuesday, March 14, 2017 11:15AM - 11:27AM |
F42.00001: Very efficient electrical spin injection into quantum dots at zero magnetic field. Pierre Renucci, Fabian Cadiz, Philippe Barate, Delphine Lagarde, Shiheng Liang, Bingshan tao, Julien Frougier, Yuan Lu, Bo Xu, Henri Jaffres, Zg Wang, X Fhan, Michel Hehn, Stephane Mangin, Jean-Marie George, Thierry Amand, Xavier Marie, Bernhard Urbaszek We have demonstrated for the first time at zero magnetic field a very efficient electrical spin injection into p-doped InAs/GaAs quantum dots (around one hole per dot in average) thanks to an ultrathin CoFeB (a few atomic planes)/MgO spin injector, presenting perpendicular magnetic anisotropy. The circular polarization of the electroluminescence (EL) emitted by the Spin Light Emitting Diode (spinLED) follows the hysteresis cycle of the magnetic layer. At zero magnetic field, a Circular polarization as large as 22 percent is measured at low temperature, far above the values usually observed at zero magnetic field for spinLEDs. The dependence of the EL circular polarization rate on current intensity and on its duty cycle is investigated, in order to track the possible nuclear polarization of the nuclei in the dots. [Preview Abstract] |
Tuesday, March 14, 2017 11:27AM - 11:39AM |
F42.00002: Dependence of the magneto-optical properties on laser excitation in magnetic QDs Peiyao Zhang, Tenzin Norden, Arman Najafi, Biplob Barman, Yutsung Tsai, Bruce McCombe, Athos Petrou, Wun-Jhong Fan, Wu-Ching Chou We compare the red shift of the PL peak energy with magnetic field in: a) ZnTe QDs embedded in an ZnMnSe matrix and b) ZnMnTe QDs embedded in a ZnSe matrix using two photon energies: 1. Excitation at 405 nm (3.06 eV) with photon energy above the ZnSe and ZnMnSe matrix gaps resulting in electron-hole pairs mainly in the matrices. 2. Excitation at 488 nm (2.54 eV) with photon energy below the ZnSe and ZnMnSe matrix gaps but above the bandgaps of the ZnTe and ZnMnTe QDs resulting in electron hole pairs exclusively in the QDs. The red shift of PL peak energy from the ZnTe QDs increases with 488 nm excitation compared to the red shift using 405 nm excitation; the trend is reversed for ZnMnTe QDs. These results are interpreted in terms of the dependence of the confinement potentials with laser photon energy. [Preview Abstract] |
Tuesday, March 14, 2017 11:39AM - 11:51AM |
F42.00003: Investigation of Mn Dopant Induced Electronic Band Structure Widening in PbS Quantum Dot Thin Films. Artem Pimachev, Andrew Yost, Gaurab Rimal, Jinke Tang, Yuri Dahnovsky, TeYu Chien A thorough understanding of the phenomena associated with doping of transition metals in semiconductors is important for the development of semiconducting electronic technologies. Furthermore, understanding the electronic interactions of TM dopants in dilute magnetic semiconductors can provide insight into magnetic phenomena. Here we present STM and spectroscopy studies of the effects of Mn doping on the energy band structures of PbS semiconducting QD thin films. As a result of Mn doping, an increase of the electronic band gap was observed. Furthermore two distinct contrasts in dI/dV mapping were discovered and it is argued through the use of DFT calculations that these are due to the type of doping mechanism, either substitutional or interstitial. We also found the dependence on the location of the Mn atoms, either on the surface or inside the thin film, and on the magnetic spin orientation. [Preview Abstract] |
Tuesday, March 14, 2017 11:51AM - 12:27PM |
F42.00004: On-demand generation of entangled multiphoton states from a confined spin in a semiconductor quantum dot Invited Speaker: Emma Schmidgall Photonic cluster states are a resource for measurement-based quantum computation, where calculations are performed by single photon measurements. We use a spin confined in a semiconductor quantum dot to deterministically generate long strings of polarization entangled photons in a cluster state by periodic timed excitation of this precessing matter qubit. In each period, an entangled photon is added to the cluster state formed by the matter qubit and the previously emitted photons. In our prototype device, the qubit is the confined dark exciton, and it produces strings of hundreds of photons in which the entanglement persists over five sequential photons. The measured process map characterizing the device has a fidelity of 0.81 with that of an ideal device. Further feasible improvements of this device may reduce the resources needed for optical quantum information processing. [Preview Abstract] |
Tuesday, March 14, 2017 12:27PM - 12:39PM |
F42.00005: The exchange-only singlet-only spin qubit Jeroen Danon, Arnau Sala In order to overcome the practical challenge of creating highly localized magnetic fields, the proposed implementations of spin qubits in semiconductor quantum dots have seen a gradual development from conceptually simple single-dot single-spin systems to more complicated triple-dot three-spin qubits that, due to the exchange interaction between the spins, can be fully operated by electric fields only. The main bottleneck for further improvement of such qubits in high-quality III-V materials is set by the fluctuating nuclear spins of the host material, resulting in slowly fluctuating random effective magnetic fields acting on the three spins. Since these fields couple into the qubit subspace, they contribute to qubit decoherence, typically yielding a $T_2^*$ of tens of ns. We propose a simple solution to this problem: After adding one more spin to the setup, one can define the qubit in a four-spin singlet-only subspace which is to lowest order insensitive to the effective nuclear fields. We suggest a feasible quadruple-dot implementation of this idea and indicate how such a qubit could be initialized, manipulated, and read out using electric fields only. [Preview Abstract] |
Tuesday, March 14, 2017 12:39PM - 12:51PM |
F42.00006: Observation of Mollow Triplets with Tunable Interactions in Double Lambda Systems of Individual Hole Spins. K. G. Lagoudakis, K. A. Fischer, T. Sarmiento, P. L. McMahon, M. Radulaski, J. L. Zhang, Y. Kelaita, C. Dory, K. M. Mueller, J. Vuckovic Although individual spins in quantum dots have been extensively used as qubits, their investigation under strong resonant driving in view of accessing Mollow physics is still an open question. We have grown high quality positively charged quantum dots (QD) embedded in a planar microcavity that enable enhanced light matter interactions. Applying a strong magnetic field in the Voigt configuration, individual positively charged quantum dots provide a double lambda level structure. Using a combination of above band and resonant excitation, we observe the formation of Mollow triplets. We investigate the regime where the Mollow sideband splittings are equal to the Zeeman splitting; we observe strong interactions between the Mollow sidebands of the inner transitions and the outer transitions in the form of very clear anticrossings. We investigated these anticrossings and we were able to modify the observed anticrossing splittings on demand by rotating the polarization of the resonant laser. We also developed a quantum-optical model of our system that fully captures the experimentally observed spectra and provides insight on the complicated level structure that results from the strong driving of our positively charged quantum dot. [Preview Abstract] |
Tuesday, March 14, 2017 12:51PM - 1:03PM |
F42.00007: Abstract Withdrawn
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Tuesday, March 14, 2017 1:03PM - 1:15PM |
F42.00008: Electron Spin Relaxation in a Transition-Metal Dichalcogenide Quantum Dot Alexander Pearce, Guido Burkard We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer. These materials provide an interesting and promising arena for quantum dot nano-structures due to combination of spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits, at low B-fields combined spin-valley Kramers qubits and at large B-fields spin qubits. Then we will discuss the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. Rashba spin-orbit admixture mechanisms allow for relaxation by in-plane phonons arising either from the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons allow for relaxation. We find that the relaxation rates scale as $\propto B^5$ and $\propto B^3$ for in-plane phonons coupling via deformation potential and piezoelectric coupling respectively, while relaxation due to the direct spin-phonon coupling scales as $\propto B^2$. In the low B-field regime we also discuss the role of impurity mediated spin relaxation which will arise in disordered quantum dots. [Preview Abstract] |
Tuesday, March 14, 2017 1:15PM - 1:27PM |
F42.00009: Abstract Withdrawn
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Tuesday, March 14, 2017 1:27PM - 1:39PM |
F42.00010: Spin-orbit coupling effects in ZB InSb and WZ InAs nanowires using multiband $\mathbf{k}\cdot\mathbf{p}$ method Tiago Campos, Paulo Eduardo Faria Junior, Martin Gmitra, Guilherme Matos Sipahi, Jaroslav Fabian We perform comprehensive numerical calculations of spin-orbit effects in semiconductor nanowires. In particular, we focus on zinc-blende InSb and wurtzite InAs semiconductors, and employ realistic $\mathbf{k}\cdot\mathbf{p}$ models fitted to first-principles band structures [1], to obtain spin-orbit spin splittings of the electronic subbands for square, circular, and hexagonal nanowires. In addition to the bulk-inversion asymmetry spin-orbit fields (Dresselhaus in zinc-blende and Rashba in wurtzite phases), we also apply a transverse electric field to induce Rashba spin splittings caused by structure inversion asymmetry. We fit the numerical band structures to symmetry-based effective Hamiltonians and obtain important materials parameters for the lowest subbands, including the spin-orbit spin splitting magnitudes and spin textures. Our work is important in the current research related to Majorana states in semiconductor nanowires. [1] FARIA JUNIOR, P. E. et al. Realistic multiband $\mathbf{k}\cdot\mathbf{p}$ approach from ab initio and spin-orbit coupling effects of InAs and InP in wurtzite phase. Physical Review B 93, 235204 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 1:39PM - 1:51PM |
F42.00011: Spin and charge transport through 1D Moire Crystals Clement Barraud, Romeo Bonnet, Pascal Martin, Maria Luisa Della Rocca, Philippe Lafarge Multiwall carbon nanotubes are good candidates for propagating spin information over large distances due to the large mobility of the carriers and to the weak spin-orbit coupling and hyperfine interactions. In this talk, I will present an experimental study concerning charge and spin transport through large diameter multiwall carbon nanotubes presenting intershell interactions leading to superlattice effects (1D Moire). After a description of 1D Moire crystals and to the implication of such superlattices in quantum transport, I will show that spin transport seems to be very efficient close to the new van Hove singularities. Clear magnetoresistance signals of the order of 40 {\%} are reported at low temperatures. [Preview Abstract] |
Tuesday, March 14, 2017 1:51PM - 2:03PM |
F42.00012: Unusual hole Rashba spin splitting in one-dimensional semiconductor nanowires Jun-Wei Luo, Shu-Shen Li, Alex Zunger By means of atomistic pseudopotential calculations we explore the evolution of the hole Rashba effect in semiconductor nanowires across the wide range of external electric fields and nanowire sizes. We uncover an abrupt transition from the steep rise, with a slope 300 times larger than the electron counterpart, to the saturation in the hole Rashba effect ($\alpha_R$) as increasing the electric field in nanowires. We reveal that the origin underlying the transition arises from the competition between quantum confinement and quantum confine stark effects on the energy separation between hole subbands. The abrupt transition to saturation gives rise to otherwise giant hole Rashba effect a moderate field-independent $\alpha_R$ for a nanowire once the electric field exceeding the transition point. In particularly, the saturated hole $\alpha_R$ in Si nanowires, which is about 100 meV{\AA} and even stronger than InAs electron Rashba effect, is almost independent on nanowire size, making Si nanowires compelling for the realization of scalable integration of Si CMOS compatible spintronic devices. [Preview Abstract] |
Tuesday, March 14, 2017 2:03PM - 2:15PM |
F42.00013: Systematic study of spin transport in Si nanowires with axial doping gradient Konstantinos Kountouriotis, Jorge Barreda, Tim Keiper, Mei Zhang, Peng Xiong Spin transport experiments have been widely employed to study spin relaxation mechanisms in bulk and two-dimensional semiconductors. Quasi 1D systems such as semiconductor nanowires (NWs) could offer some advantages as spin transport channels; it was predicted that quantum confinement can lead to significant enhancement in spin lifetime and diffusion lengths. We have performed systematic spin transport, including local 2T, 3T, and nonlocal 4T spin valve measurements, in phosphorus-doped Si NWs exhibiting a pronounced doping gradient along the axial direction. The doping gradient enables the formation of Ohmic contacts and Schottky barriers of different widths and heights between a series of ferromagnetic electrodes and a single NW. This facilitates a methodical study of the dependence of the spin signal on interfacial resistance. Spin injection/extraction is effective within a window of interfacial resistance, which in our devices corresponds to zero-bias 2T resistances between 100 k$\Omega $ and 2 M$\Omega $, corresponding to the estimated carrier densities between 6.8$\times$ 10$^{\mathrm{17}}$ cm$^{\mathrm{-3}}$ and 4.5$\times$ 10$^{\mathrm{18}}$ cm$^{\mathrm{-3}}$. Within this region we measured nonlocal spin signals of magnitudes between 1 $\mu $V and 50 $\mu $V (at I$=$20 nA). Also, the spin signals are observed to increase when the spins are injected from a more resistive interface. Comparison of the local 2T and nonlocal 4T signals and the effects of interchanging the injector and detector electrodes for the same transport channel will be presented. *Work supported by NSF Grant DMR-1308613. [Preview Abstract] |
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