Photon-assisted Andreev transport and sub-gap structures

We report new measurements of microwave-induced perturbations of the sub-harmonic energy gap structures in the current-voltage characteristics of superconductor-semiconductor-superconductor junctions. Around the sub-gap bias voltages associated with the enhanced quasi-particle transfer mediated by multiple Andreev reflection processes we observe microwave induced satellites, shifted in voltage by multiples of hf/en, where hf is the photon energy and n is the number of quasi-particle traversals as determined by the Andreev processes.

The observed behavior is the analogue of the so-called photon-assisted tunneling but here associated with the multiple Andreev reflections. (C) 2000 Elsevier Science B.V. All rights reserved.