Microscopic theory of nonstationary tunnel current in a superconducting junction

Theory of nonstationary tunnel current which is not based on the tunnel Hamiltonian. The system of equations for one-time correlation functions is used. Its solution is obtained by means of the perturbation theory in the transparency and the assumption of the local equilibrium with respect to time of the statistical operator in the zeroapproximation is also used, its time dependence being determined by the only “hydrodynamical” variable, the coherent phase difference. The expression for the tunnel current in the first order in the transparency is obtained.