Phase-sensitive transport at a normal metal–superconductor interface close to a Josephson junction

Abstract

Phase- and voltage bias-sensitive quasiparticle transport at a double NIS1IS2 interface is considered. The barriers I range from tunnel to transparent, and the intermediate region S1 has a width comparable to the superconducting coherence length. A phase difference φ is applied to the Josephson junction S1IS2. The normal and Andreev reflections at the NIS1 interface become φ sensitive, and transport is governed by interferences within the narrow S1 region in both the normal and the anomalous channels. The subgap conductance is separately (energy E) and (phase φ) symmetric. Above the superconducting gap, the conductance is, in general, not symmetric even if (E,φ) is changed in (−E,−φ), but the symmetry is restored by averaging Fermi oscillations. The Tomasch oscillations are amplified by the phase difference. The subgap conductance exhibits a resonant structure at the energy of the Andreev bound states (ABSs) of the S1IS2 junction, providing a side spectroscopy of such states. Depending on the relative transparencies of the junctions, the resonance can increase or reduce the conductance, and it can even vanish for φ=π, featuring total reflection of quasiparticles at NS1 by the ABS at S1S2.

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