Ultraclean Andreev interferometers

Coupling a two-terminal Josephson junction to the stationary modes of the electromagnetic field produces the so-called Fiske resonances. Here, we propose another mechanism based on the exchange between the static Andreev bound states (ABS) and a nonequilibrium Fermi surface in an ultraclean multiterminal device. As a simple model, we consider an effective S_a-N_eff-S_b double junction connecting the superconductors S_a and S_b to the infinite central normal metal N_eff. We find that the underlying microscopic process of phase-sensitive Andreev reflection (phase-AR) produces the possibility of an inversion, that is, the conductance can be larger at half-flux quantum than in zero field. The inversion-noninversion alternate as the bias voltage is increased. In addition, if the central region N_eff is an integrable billiard connected to an infinite normal reservoir, we find that the standard ABS are replaced by one- and two-particle Andreev resonances that can be probed by the bias voltage. Finally, we find that, in the corresponding all-superconducting Andreev interferometer, the superconducting gap produces protection against the short relaxation time of the quasiparticle continua if the time periodic dynamics is treated as a perturbation. The spectrum of the two-particle resonances is then sparse inside the spectrum of the pairs of one-particle resonances. Our work supports the nonFloquet intrinsic resonances in two-dimensional metal-based Andreev interferometers, and challenges the Floquet theory of multiterminal Josephson junctions.