Microscopic theory of the phase-dependent linear conductance in highly transmissive superconducting quantum point contacts

A microscopic theory for transport properties of a superconducting quantum point contact is presented. According to contact transmission and quasiparticle damping two different physical regimes can be identified. In the limit of small applied voltages and weak damping this theory provides an exact analytical expression for the current through the contact. The phase-dependent linear conductance thus obtained exhibits an unusual behavior at low temperatures which strongly differs from the standard cos phi-like form. It is argued that a realistic highly transmissive contact will be accurately described by our analytical expression.