ANOMALOUS TEMPERATURE-DEPENDENCE OF THE SUPERCURRENT THROUGH A CHAOTIC JOSEPHSON-JUNCTION

We calculate the supercurrent through a Josephson junction consisting of a phase-coherent metal particle (quantum dot), weakly coupled to tw o superconductors. The classical motion in the quantum dot is assumed to be chaotic on time scales greater than the ergodic time tau(erg), w hich itself is much smaller than the mean dwell time tau(dwell). The e xcitation Spectrum of the Josephson junction has a gap E-gap, which ca n be less than the gap Delta in the bulk superconductors. The average supercurrent is computed in the ergodic regime tau(erg) much less than (h) over bar/Delta, using random-matrix theory, and in the non-ergodi c regime tau(erg) much greater than (h) over bar/Delta, using a semicl assical relation between the supercurrent and dwell-time distribution. In contrast to conventional Josephson junctions, raising the temperat ure above the excitation gap does not necessarily lead to an exponenti al suppression of the supercurrent. Instead, we find a temperature reg ime between E-gap and Delta where the supercurrent decreases logarithm ically with temperature. This anomalously weak temperature dependence is caused by long-range correlations in the excitation spectrum, which extend over an energy range (h) over bar/tau(erg) greater than E-gap similar or equal to (h) over bar/tau(dwell). A similar logarithmic tem perature dependence of the supercurrent was discovered by Aslamazov, L arkin and Ovchinnikov in a Josephson junction consisting of a disorder ed metal between two tunnel barriers. (C) 1997 Elsevier Science Ltd.