title: Subharmonic shapiro steps and assisted tunneling in superconducting point contacts.
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 V = (m/n)h(omega)(r)/2e, where n,m are integer numbers and omega(r) is the radiation frequency. The subharmonic steps (n not equal 1) 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.
authors.affiliation: Institut für Theoretische Festkörperphysik, Universität Karlsruhe, 76128 Karlsruhe, Germany.
authors.forename: J C
authors.initials: JC
authors.lastname: Cuevas
authors.forename: J
authors.initials: J
authors.lastname: Heurich
authors.forename: A
authors.initials: A
authors.lastname: Martín-Rodero
authors.forename: A
authors.initials: A
authors.lastname: Levy Yeyati
authors.forename: G
authors.initials: G
authors.lastname: Schön