Dissipative electron transport through Andreev interferometers

Phys Rev B, 1997

We present experiments revealing a singularity in the coherent current across a superconductor/ semiconductor/superconductor ͑SSmS͒ junction at the bias voltage corresponding to the superconducting energy gap Vϭ⌬/e. The SSmS structure consists of highly doped GaAs with superconducting electrodes of aluminum configured as an interferometer. The phase-coherent component of the current is probed as the amplitude of h/2e vs magnetic-field oscillations in the differential resistance of the interferometer.

Physical Review B, 1997

We present experiments revealing a singularity in the coherent current across a superconductor/ semiconductor/superconductor ͑SSmS͒ junction at the bias voltage corresponding to the superconducting energy gap Vϭ⌬/e. The SSmS structure consists of highly doped GaAs with superconducting electrodes of aluminum configured as an interferometer. The phase-coherent component of the current is probed as the amplitude of h/2e vs magnetic-field oscillations in the differential resistance of the interferometer.

Phys Rev B, 1997

We present experiments revealing a singularity in the coherent current across a superconductor/semiconductor/superconductor (SSmS) junction at the bias voltage corresponding to the superconducting energy gap V=Δ/e. The SSmS structure consists of highly doped GaAs with superconducting electrodes of aluminum configured as an interferometer. The phase-coherent component of the current is probed as the amplitude of h/2e vs magnetic-field oscillations in the differential resistance of the interferometer.

Physica C: Superconductivity, 2001

We observed superconductivity-induced conductance oscillations, arising from quasiparticle interference eects in a single normal-metallic (N) electrode of ®nite width in contact with a superconductor (S). A 10 Â 10 lm 2 Al patch was overlaid on a pre-evaporated 0.5-lm-wide mesoscopic silver wire. A phase gradient along the N/S interface was induced by applying a magnetic ®eld perpendicular to the plane of the superconducting Al patch. The conductance across the N/S interface showed Fraunhofer-like oscillations with amplitudes of a small fraction of 2e 2 =h per conducting channel, for ®elds up to 450 G. For suciently low ®elds and temperatures the interfacial diraction eect of quasiparticles is more complicated due to the ®eld-induced electron±hole dephasing eect. None the less, the overall feature of the oscillatory magnetoconductance from the N/S interface appears to con®rm the diraction of Andreev-re¯ected quasiparticles proposed theoretically for a single N/S interface with a phase gradient.

Physical Review B - PHYS REV B, 1999

We measure the resistance of a normal mesoscopic sample with two superconducting mirrors and find two regimes with qualitatively different behavior. At temperatures below 90 mK peaks in the conductance were found when the phase difference between the two superconductors is an odd multiple of pi. The peak heights increase with decreasing temperature. Above 100 mK the observed peaks give way to dips in the conductance. While the high-temperature behavior can be explained in terms of the thermal effect [Phys. Rev. Lett. 76, 823 (1996)], we propose that the low-temperature behavior is a manifestation of resonant transmission of low-energy quasiparticles through Andreev states.

Journal of Physics: Condensed Matter, 1996

Physical Review B, 2002

Andreev reflection between a normal metal and a superconductor whose order parameter exhibits quantum phase fluctuations is examined. The approach chosen is non perturbative in the tunneling Hamiltonian, and enables to probe the whole range of voltage biases up to the gap amplitude. Results are illustrated using the one-dimensional Josephson junction array model previously introduced in the linear response regime. Phase fluctuations are shown to affect the differential conductance and are compared to the result of Blonder, Tinkham and Klapwijk for a rigid BCS superconductor. The noise spectrum of the Andreev current is also obtained and its second derivative with respect to frequency is proposed as a direct tool to analyze the phase fluctuations.

Physica B: Condensed Matter, 1994

An overview of microscopic current-voltage relations applicable to mesoscopic superconductors is presented. These are used to examine a variety of new phenomena, including the change 8G in the two-probe electrical conductance G of a mesoscopic sample due to the switching on of superconductivity. It is predicted that 8G can have an arbitrary, sample dependent sign, have a magnitude much greater than 2e2/h and is suppressed by the application of a magnetic field. For an Andreev phase gradiometer formed by attaching a finite width normal wire at 90 ° to a superconductor, it is predicted that due to quantum interference from an order parameter phase gradient, the conductance of the wire will be an oscillatory function of the supercurrent. For an Andreev interferometer obtained by embedding a pair of superconductors with an order parameter phase difference $, in a disordered normal host, it is predicted that the phase periodic conductance G(~b) may have a maximum or a minimum at q~ = 0. In addition, the amplitude of the ensemble-averaged, 2rt periodic Fourier component decreases with energy, suggesting the possibility of a cross-over from a 2n to n periodicity with increasing temperature. Finally for a T-shaped normal structure, with a superconducting island located on the vertical leg and a current passing horizontally from left to right, it is predicted that the differential conductance exhibits a slow oscillatory dependence on the position of the superconductor and on the applied voltage.

Physical Review B, 2009

We analyze the non-local transport properties of a d-wave superconductor coupled to metallic electrodes at nanoscale distances. We show that the non-local conductance exhibits an algebraical decay with distance rather than the exponential behavior which is found in conventional superconductors. Crossed Andreev processes, associated with electronic entanglement, are favored for certain orientations of the symmetry axes of the superconductor with respect to the leads. These properties would allow its experimental detection using present technologies.

Journal of Computational and Theoretical Nanoscience, 2008

We have investigated the quantum transport through the Superconductor-Semiconductor mesoscopic interface in the presence of an external radiation field. The current spectrum is analyzed as a function of the frequency and the temperature. The current-voltage (I-V) characteristics were found to be very sensitive to the photon frequency. Additionally, photon-assisted transport in our system is very robust: The one-photon channel remains up to low temperature, which implies that these structures support gain at THz frequencies even at 9 K. The resonances sit on a background current which it is deeply modified, as a result of photon assisted multiple Andreev reflections. The results render rigid support for the full quantum theory of transport between two superconductors based on the idea of Andreev bound states.