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Observation of photon-assisted noise in a diffusive normal metal-superconductor junction
Kozhevnikov1, Schoelkopf, Prober
1Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06520-8284, USA.
Abstract:
We report measurements of nonequilibrium noise in a diffusive normal metal-superconductor (N-S) junction in the presence of both dc bias and high-frequency ac excitation. We find that the shot noise of a diffusive N-S junction is doubled compared to a normal diffusive conductor. Under ac excitation of frequency nu the shot noise develops features at bias voltages |V| = hnu/(2e), which bear all the hallmarks of a photon-assisted process. Observation of these features provides clear evidence that the effective charge of the current carriers is 2e, due to Andreev reflection.
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