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 Sₐ-Neff-Sb double junction connecting the superconductors Sₐ and Sb to the infinite central normal metal Neff. 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 Neff 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.