Abstract
We analyze the current in a superconducting point contact of arbitrary transmission in the presence of a microwave radiation. The interplay between the ac Josephson current and the microwave signal gives rise to Shapiro steps at voltages , where are integer numbers and is the radiation frequency. The subharmonic steps ( ) are a consequence of multiple Andreev reflections (MAR) and provide a signature of the peculiar ac Josephson effect at high transmission. Moreover, the dc current exhibits a rich subgap structure due to photon-assisted MARs.
- Received 8 September 2001
DOI:https://doi.org/10.1103/PhysRevLett.88.157001
©2002 American Physical Society