Spin Hall effects due to phonon skew scattering

A diversity of spin Hall effects in metallic systems is known to rely on Mott skew scattering. In this work its high-temperature counterpart, phonon skew scattering, which is expected to be of foremost experimental relevance, is investigated. In particular, the phonon skew scattering spin Hall conductivity is found to be practically $T$-independent for temperatures above the Debye temperature $T_D$. As a consequence, in Rashba-like systems a high-$T$ linear behavior of the spin Hall angle demonstrates the dominance of extrinsic spin-orbit scattering only if the intrinsic spin splitting is smaller than the temperature.Comment: Accepted version, 4 (+1) pages, 2 figure

Room temperature spin thermoelectrics in metallic films

Considering metallic films at room temperature, we present the first theoretical study of the spin Nernst and thermal Edelstein effects which takes into account dynamical spin-orbit coupling, i.e., direct spin-orbit coupling with the vibrating lattice (phonons) and impurities. This gives rise to two novel processes, namely a dynamical Elliott-Yafet spin relaxation and a dynamical side-jump mechanism. Both are the high-temperature counterparts of the well-known $T = 0$ Elliott-Yafet and side-jump, central to the current understanding of the spin Hall, spin Nernst and Edelstein effects at low $T$. We consider the experimentally relevant regime $T > T_D$, with $T_D$ the Debye temperature, as the latter is lower than room temperature in transition metals such as Pt, Au and Ta typically employed in spin injection/extraction experiments. We show that the interplay between intrinsic (Bychkov-Rashba type) and extrinsic (dynamical) spin-orbit coupling yields a nonlinear $T$- dependence of the spin Nernst and spin Hall conductivities.Comment: 9 pages, 4 figure

Using Activated Transport in Parallel Nanowires for Energy Harvesting and Hot Spot Cooling

12 pages, 8 figures, 4 appendicesInternational audienceWe study arrays of parallel doped semiconductor nanowires in a temperature range where the electrons propagate through the nanowires by phonon assisted hops between localized states. By solving the Random Resistor Network problem, we compute the thermopower $S$, the electrical conductance $G$, and the electronic thermal conductance $K^e$ of the device. We investigate how those quantities depend on the position -- which can be tuned with a back gate -- of the nanowire impurity band with respect to the equilibrium electrochemical potential. We show that large power factors can be reached near the band edges, when $S$ self-averages to large values while $G$ is small but scales with the number of wires. Calculating the amount of heat exchanged locally between the electrons inside the nanowires and the phonons of the environment, we show that phonons are mainly absorbed near one electrode and emitted near the other when a charge current is driven through the nanowires near their band edges. This phenomenon could be exploited for a field control of the heat exchange between the phonons and the electrons at submicron scales in electronic circuits. It could be also used for cooling hot spots

Quasiclassical approach and spin-orbit coupling

We discuss the quasiclassical Green function method for a two-dimensional electron gas in the presence of spin-orbit coupling, with emphasis on the meaning of the $\xi$-integration procedure. As an application of our approach, we demonstrate how the spin-Hall conductivity, in the presence of spin-flip scattering, can be easily obtained from the spin-density continuity equation.Comment: 3 pages, Submitted to Physica

Gate-modulated thermopower of disordered nanowires: II. Variable-range hopping regime

International audienceWe study the thermopower of a disordered nanowire in the field effect transistorconfiguration. After a first paper devoted to the elastic coherent regime (Bosisio R., Fleury G.and Pichard J.-L. 2014 New J. Phys. 16 035004), we consider here the inelastic activated regimetaking place at higher temperatures. In the case where charge transport is thermally assisted byphonons (Mott Variable Range Hopping regime), we use the Miller-Abrahams random resistornetwork model as recently adapted by Jiang et al. for thermoelectric transport. This approachpreviously used to study the bulk of the nanowire impurity band is extended for studying itsedges. In this limit, we show that the typical thermopower is largely enhanced, attaining valueslarger that 10 kB/e ∼ 1 mV K−1 and exhibiting a non-trivial behaviour as a function of thetemperature. A percolation theory by Zvyagin extended to disordered nanowires allows us toaccount for the main observed edge behaviours of the thermopower

Towards a quantum time mirror for non-relativistic wave packets

We propose a method – a quantum time mirror (QTM) – for simulating a partial time-reversal of the free-space motion of a nonrelativistic quantum wave packet. The method is based on a short-time spatially-homogeneous perturbation to the wave packet dynamics, achieved by adding a nonlinear time-dependent term to the underlying Schroedinger equation. Numerical calculations, supporting our analytical considerations, demonstrate the effectiveness of the proposed QTM for generating a time-reversed echo image of initially localized matter-wave packets in one and two spatial dimensions. We also discuss possible experimental realizations of the proposed QTM

Overcoming dispersive spreading of quantum wave packets via periodic nonlinear kicking

We propose the suppression of dispersive spreading of wave packets governed by the free-space Schrodinger equation with a periodically pulsed nonlinear term. Using asymptotic analysis, we construct stroboscopically-dispersionless quantum states that are physically reminiscent of, but mathematically different from, the well-known one-soliton solutions of the nonlinear Schrodinger equation with a constant (time-independent) nonlinearity. Our analytics are strongly supported by full numerical simulations. The predicted dispersionless wave packets can move with arbitrary velocity and can be realized in experiments involving ultracold atomic gases with temporally controlled interactions

Quasiclassical approach to the spin-Hall effect in the two-dimensional electron gas

We study the spin-charge coupled transport in a two-dimensional electron system using the method of quasiclassical ($\xi$-integrated) Green's functions. In particular we derive the Eilenberger equation in the presence of a generic spin-orbit field. The method allows us to study spin and charge transport from ballistic to diffusive regimes and continuity equations for spin and charge are automatically incorporated. In the clean limit we establish the connection between the spin-Hall conductivity and the Berry phase in momentum space. For finite systems we solve the Eilenberger equation numerically for the special case of the Rashba spin-orbit coupling and a two-terminal geometry. In particular, we calculate explicitly the spin-Hall induced spin polarization in the corners, predicted by Mishchenko et al. [13]. Furthermore we find universal spin currents in the short-time dynamics after switching on the voltage across the sample, and calculate the corresponding spin-Hall polarization at the edges. Where available, we find perfect agreement with analytical results.Comment: 9 pages, 6 figure

Steering Zitterbewegung in driven Dirac systems: From persistent modes to echoes

Although Zitterbewegung—the jittery motion of relativistic particles—was known since 1930 and was predicted in solid-state systems long ago, it has been directly measured so far only in so-called quantum simulators, i.e., quantum systems under strong control, such as trapped ions and Bose-Einstein condensates. A reason for the lack of further experimental evidence is the transient nature of wave-packet Zitterbewegung. Here, we study how the jittery motion can be manipulated in Dirac systems via time-dependent potentials with the goal of slowing down/preventing its decay or of generating its revival. For the harmonic driving of a mass term, we find persistent Zitterbewegung modes in pristine, i.e., scattering free, systems. Furthermore, an effective time-reversal protocol—the “Dirac quantum time mirror”—is shown to retrieve Zitterbewegung through echoes