Dr Shu Suzuki, Nagoya University

Long-range coherence in spin-triplet superconducting junctions

The proximity effect, penetration of Cooper pairs, is one of the fascinating phenomena occurring in diffusive-normal-metal (DN)/superconductor (SC) functions. The length scale of the proximity effect is characterised by the thermal coherence length  xi_T. Therefore, phase-coherent effects such as the Josephson effect are, in principle, negligible when the spacing between the two SCs L is much longer than xi_T. However, Volkov and Takayanagi showed that, even when L>>xi_T, the conductance of the junction depends on the phase difference between the SCs [1,2]. Namely, interferences occur in a longer length scale than xi_T. The method they employed is the so-called weak-proximity-effect approximation, in which the Cooper pairs in the DN is assumed to be spin-singlet s-wave. Therefore, whether and how the long-range coherence effect occurs in a junction with a spin-triplet Cooper pairs has been still unclear. In this study [3], DN/SC/DN/SC/DN junctions are considered, where SC is either of a singlet or triplet SC. The energy spectra are obtained numerically from the Usadel Green's function. It is shown that, for a triplet p-wave junction, the zero-energy peak spreads between the two SCs even when L>>xi_T. Moreover, the decay length for triplet SCs are not simply determined by the phase.

Location: Tolansky Building (room T125)