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We show here theoretically and experimentally that a Rashba-split electron state inside a ferromagnet can efficiently convert a dynamical spin accumulation into an electrical voltage. The effect is understood to stem from the Rashba splitting but with a symmetry linked to the magnetization direction. It is experimentally measured by spin pumping in a CoFeB/MgO structure where it is found to be as efficient as the inverse spin Hall effect at play when Pt replaces MgO, with the extra advantage of not affecting the damping in the ferromagnet. more...

In ferromagnet/normal-metal bilayers, the sensitivity of the spin Hall magnetoresistance and the spin Nernst magnetothermopower to the boundary conditions at the interface is of central importance. In general, such boundary conditions can be substantially affected by current-induced spin polarizations. In order to quantify the role of the latter, we consider a Rashba two-dimensional electron gas with a ferromagnet attached to one side of the system. The geometry of such a system maximizes the effect of current-induced spin polarization on the boundary conditions, and the spin Hall magnetoresistance is shown to acquire a non-trivial and asymmetric dependence on the magnetization direction of the ferromagnet., Comment: 20 pages, 7 figures more...

We consider nanowires in the field effect transistor device configuration. Modeling each nanowire as a one dimensional lattice with random site potentials, we study the heat exchanges between the nanowire electrons and the substrate phonons, when electron transport is due to phonon-assisted hops between localized states. Shifting the nanowire conduction band with a metallic gate induces different behaviors. When the Fermi potential is located near the band center, a bias voltage gives rise to small local heat exchanges which fluctuate randomly along the nanowire. When it is located near one of the band edges, the bias voltage yields heat currents which flow mainly from the substrate towards the nanowire near one boundary of the nanowire, and in the opposite direction near the other boundary. This opens interesting perspectives for heat management at submicron scales: arrays of parallel gated nanowires could be used for a field control of phonon emission/absorption. (C) 2016 Published by Elsevier B.V. more...

International audience; We review a series of works describing thermoelectric effects in gated disordered nanowires (field effect transistor device configuration). After considering the elastic coherent regime characterizing sub-Kelvin temperatures, we study the inelastic activated regime occurring at higher temperatures, where electronic transport is dominated by phonon-assisted hops between localised states (Mott variable range hopping). The thermoelectric effects are studied as a function of the location of the Fermi level inside the nanowire conduction band, notably around its edges where they become very large. We underline the interest of using electron-phonon coupling around the band edges of large arrays of parallel nanowires for energy harvesting and hot spot cooling at small scales. Multiterminal thermoelectric transport and ratchet effects are eventually considered in the activated regime. more...

We study arrays of disordered nanowires arranged in parallel and in contact between two metallic electrodes. If one adjusts with a back gate the chemical potential to one edge of the impurity band, these arrays open promising perspectives for energy harvesting and heat management in a temperature range where the electrons propagate inside the nanowires by phonon assisted hops between localized states. On one hand, the thermopower self-averages to large values while the electrical conductance scales with the number of nanowires. This gives large power factors and suitable figures of merit for the thermoelectric conversion. On the other hand, the phonons are mainly absorbed near one electrode and emitted near the other. This phenomenon can be exploited for cooling hot spots in electronic circuits. more...

We study the thermopower of a disordered nanowire in the field effect transistor configuration. After a first paper devoted to the elastic coherent regime (Bosisio, Fleury and Pichard 2014 New J. Phys. 16 035004), we consider here the inelastic activated regime taking place at higher temperatures. In the case where the charge transport is thermally assisted by phonons (Mott Variable Range Hopping regime), we use the Miller–Abrahams random resistor network model as recently adapted by Jiang et al for thermoelectric transport. This approach, previously used to study the bulk of the nanowire impurity band, is extended for studying its edges. In this limit, we show that the typical thermopower is largely enhanced, attaining values larger than $10\;{{k}_{{\rm B}}}/e\sim 1\;{\rm mV}\;{{{\rm K}}^{-1}}$ and exhibiting a non-trivial behaviour as a function of the temperature. A percolation theory by Zvyagin extended to disordered nanowires allows us to account for the main observed edge behaviours of the thermopower. more...

We study a thermoelectric ratchet consisting of an array of disordered nanowires arranged in parallel on top of an insulating substrate and contacted asymmetrically to two electrodes. Transport is investigated in the Mott hopping regime, when localized electrons can propagate through the nanowires via thermally assisted hops. When the electronic temperature in the nanowires is different from the phononic one in the substrate, we show that a finite electrical current is generated even in the absence of driving forces between the electrodes. We discuss the device performance both as an energy harvester, when an excess heat from the substrate is converted into useful power, and as a refrigerator, when an external power is supplied to cool down the substrate. more...

We review a series of works describing thermoelectric effects in gated disordered nanowires (field effect transistor device configuration). After considering the elastic coherent regime characterizing sub-Kelvin temperatures, we study the inelastic activated regime occurring at higher temperatures, where electronic transport is dominated by phonon-assisted hops between localised states (Mott variable range hopping). The thermoelectric effects are studied as a function of the location of the Fermi level inside the nanowire conduction band, notably around its edges where they become very large. We underline the interest of using electron-phonon coupling around the band edges of large arrays of parallel nanowires for energy harvesting and hot spot cooling at small scales. Multiterminal thermoelectric transport and ratchet effects are eventually considered in the activated regime. more...