Magnetic field influence on the proximity effect in semiconductor - superconductor hybrid structures and their thermal conductance

We show that a magnetic field can influnce the proximity effect in NS junctions via diamagnetic screening current flowing in the superconductor. Using ballistic quasi-one-dimensional (Q1D) electron channels as an example, we show that the supercurrent flow shifts the proximity-induced minigap in the excitation spectrum of a Q1D system from the Fermi level to higher quasiparticle energies. Thermal conductance of a Q1D channel (normalized by that of a normal Q1D ballistic system) is predicted to manifest such a spectral feature as a nonmonotonic behavior at temperatures corresponding to the energy of excitation into the gapful part of the spectrum.Comment: 5 pages, 3 figures, revised version with a new titl

Superconducting phase tuned sample-specific conductance fluctuations

We have studied sample-specific conductance fluctuations tuned by the phase difference between superconducting boundaries attached to a T-shaped two-dimensional electron gas. In low magnetic fields, oscillations due to phase-conjugated Andreev reflections were observed with an amplitude delta G(qp)similar or equal to 0.10e(2)/h. These oscillations were suppressed by a flux of approximately h/e through the interference region. For larger magnetic fields, superconducting-phase modulated sample-specific conductance fluctuations were found with an amplitude delta Gy(Delta phi)similar or equal to.0.005e(2)/h

Nonequilibrium Josephson effect in mesoscopic ballistic multiterminal SNS junctions

We present a detailed study of nonequilibrium Josephson currents and conductance in ballistic multiterminal SNS-devices. Nonequilibrium is created by means of quasiparticle injection from a normal reservoir connected to the normal part of the junction. By applying a voltage at the normal reservoir the Josephson current can be suppressed or the direction of the current can be reversed. For a junction longer than the thermal length, $L\gg\xi_T$, the nonequilibrium current increases linearly with applied voltage, saturating at a value equal to the equilibrium current of a short junction. The conductance exhibits a finite bias anomaly around $eV \sim \hbar v_F/L$. For symmetric injection, the conductance oscillates $2\pi$-periodically with the phase difference $\phi$ between the superconductors, with position of the minimum ($\phi=0$ or $\pi$) dependent on applied voltage and temperature. For asymmetric injection, both the nonequilibrium Josephson current and the conductance becomes $\pi$-periodic in phase difference. Inclusion of barriers at the NS-interfaces gives rise to a resonant behavior of the total Josephson current with respect to junction length with a period $\sim \lambda_F$. Both three and four terminal junctions are studied.Comment: 21 pages, 19 figures, submitted to Phys. Rev.

Thermoelectric effects in superconducting proximity structures

Attaching a superconductor in good contact with a normal metal makes rise to a proximity effect where the superconducting correlations leak into the normal metal. An additional contact close to the first one makes it possible to carry a supercurrent through the metal. Forcing this supercurrent flow along with an additional quasiparticle current from one or many normal-metal reservoirs makes rise to many interesting effects. The supercurrent can be used to tune the local energy distribution function of the electrons. This mechanism also leads to finite thermoelectric effects even in the presence of electron-hole symmetry. Here we review these effects and discuss to which extent the existing observations of thermoelectric effects in metallic samples can be explained through the use of the dirty-limit quasiclassical theory.Comment: 14 pages, 10 figures. 374th WE-Heraus seminar: Spin physics of superconducting heterostructures, Bad Honnef, 200