Phase-sensitive transport at a normal metal-superconductor interface close to a Josephson junction
Résumé
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 phi is applied to the Josephson junction S1IS2. The normal and Andreev reflections at the NIS1 interface become phi-sensitive, and transport is governed by interferences within the narrow S1 region, both in the normal and anomalous channels. The subgap conductance is separately (energy E)- and (phase phi)- symmetric. Above the superconducting gap, the conductance is in general not symmetric even if $(E,phi)$ is changed in $(-E,-phi)$, 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 (ABS) 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 phi=pi, featuring total reflection of quasiparticles at NS1 by the ABS at S1S2.