On residual RF losses and tunnel currents caused by interface states

Superconducting rf cavities show large residual losses Rreswhich limit the application of such cavities Beside the coherent phonon excitation by interface states (IS), the up till now neglected incoherent phonon excitation will be discussed as cause for residual losses Rres. But IS also weaken the superconducting interaction and enhance the current through the oxide by resonance tunneling, e.g., as super, - leakage - or assisted current in tunnel junctions. Parameters influencing the IS and the residual losses, the weakening of the superconducting interaction and the enhanced tunnel currents will be worked out for Nb-Nb2O5-interfaces.