Frequency Dependent Conductance of a Tunnel Junction in the Semiclassical Limit

The linear conductance of the a small metallic tunnel junction embedded in an electromagnetic environment of arbitrary impedance is determined in the semiclassical limit. Electron tunneling is treated beyond the orthodox theory of Coulomb blockade phenomena by means of a nonperturbative path integral approach. The frequency dependent conductance is obtained from Kubo's formula. The theoretical predictions are valid for high temperatures and/or for large tunneling conductance and are found to explain recent experimental data.