Superconducting atomic contacts under microwave irradiation.
We have measured the effect of microwave irradiation on the dc current-voltage characteristics of superconducting atomic contacts. The interaction of the external field with the ac supercurrents leads to replicas of the supercurrent peak, the well-known Shapiro resonances. The observation of supplementary fractional resonances for contacts containing highly transmitting conduction channels reveals their nonsinusoidal current-phase relation. The resonances sit on a background current which is itself deeply modified, as a result of photon-assisted multiple Andreev reflections. The results provide firm support for the full quantum theory of transport between two superconductors based on the concept of Andreev bound states.
Chauvin
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Quantronics Group, Service de Physique de l'Etat Condensé (CNRS URA 2464), DSM/DRECAM, CEA-Saclay, 91191 Gif-sur-Yvette Cedex, France.
vom Stein
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Pothier
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Joyez
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Huber
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Esteve
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Urbina
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