Nonequilibrium quasiclassical theory for Josephson structures

We present a nonequilibrium quasiclassical formalism suitable for studying linear-response ac properties of Josephson junctions. The nonequilibrium self-consistency equations are satisfied, to a very good accuracy, already in zeroth iteration. We use the formalism to study ac Josephson effect in a ballistic superconducting point contact. The real and imaginary parts of the ac linear conductance are calculated both analytically (at low frequencies) and numerically (at arbitrary frequency). They show strong temperature, frequency, and phase dependences. Many anomalous properties appear near phi=pi. We ascribe them to the presence of zero energy bound states.