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Subharmonic Shapiro steps and assisted tunneling in superconducting point contacts

J. C. Cuevas·J. Heurich·A. Martin-Rodero·A. Levy Yeyati·G. Schoen
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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) \hbar ω_r/2e, where n,m are integer numbers and ω_r is the radiation frequency. The subharmonic steps (n different from 1) are a consequence of the ocurrence of multiple Andreev reflections (MAR) and provide an unambiguous signature of the peculiar ac Josephson effect at high transmission. Moreover, the dc current exhibits a rich subgap structure due to photon-assisted MARs.

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J. C. Cuevas, J. Heurich, A. Martin-Rodero, A. Levy Yeyati, G. Schoen. 2001-09-08. Subharmonic Shapiro steps and assisted tunneling in superconducting point contacts. https://doi.org/10.1103/physrevlett.88.157001

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