Nonequilibrium spin-dependent phenomena in mesoscopic superconductor–normal metal tunnel structures

Abstract

We analyze the broad range of spin-dependent nonequilibrium transport properties of hybrid systems composed of a normal region tunnel coupled to two superconductors with exchange fields induced by the proximity to thin ferromagnetic layers and highlight its functionalities. By calculating the quasiparticle distribution functions in the normal region we find that they are spin-dependent and strongly sensitive to the relative angle between exchange fields in the two superconductors. The impact of inelastic collisions on their properties is addressed. As a result, the electric current flowing through the system is found to be strongly dependent on the relative angle between exchange fields, giving rise to a huge value of magnetoresistance. Moreover, the current presents a complete spin-polarization in a wide range of bias voltages, even in the quasiequilibrium case. In the nonequilibrium limit we parametrize the distributions with an "effective" temperature, which turns out to be strongly spin-dependent, though quite sensitive to inelastic collisions. By tunnel coupling the normal region to an additional superconducting electrode we show that it is possible to implement a spin-polarized current source of both spin species, depending on the bias voltages applied. 74.50.+r,05.70.Ln

Influence of photon-assisted tunneling on heat flow in a normal metal–superconductor tunnel junction

“…Such junctions exhibit highly nonlinear current-voltage characteristics at low temperatures, and normally the current is due to quasiparticles only. NIS junctions are known to have peculiar heat transport properties under the application of a dc bias voltage, [19][20][21][22][23][24][25][26][27][28][29] or ͑"quasistatic"͒ ac radiation of relatively low frequency in form of either periodic or stochastic drive. [30][31][32] Specifically, it is possible to find operation regimes where the normal metal is refrigerated and the superconductor is overheated, and in some special situations the opposite can occur as well.…”

Spin-Resolved Tunneling Studies of the Exchange Field inEuS/AlBilayers

“…Or, perhaps, one may be able to modulate the interface exchange coupling with an external electric field via a gate. In either case, the strategy is to use a small external field to control a large exchange field in order to realize a device, such as superconducting switch or a tunable polarized current source [27].…”

Spin heat accumulation and its relaxation in spin valves

“…The latter parametrizes the spin dependence of the energy distribution functions f ͑E͒, whose description also requires spin-dependent temperatures T . 2,3 As shown below, these should in general be interpreted as effective parameters.In this Rapid Communication we describe the processes affecting the T and through them the thermoelectric response in spin valves, which we find to be a sensitive probe for the nonequilibrium state in the nonmagnetic spacer. Whereas the spin accumulation relaxes only by scattering processes that break spin rotation invariance such as spinorbit interaction and magnetic disorder, the spin heat accumulation T s = T ↑ − T ↓ is sensitive also to electron-phonon ͑e-ph͒ and electron-electron ͑e-e͒ interactions.…”