title: Observation of photon-assisted noise in a diffusive normal metal-superconductor junction
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.
authors.affiliation: Departments of Physics and Applied Physics, Yale University, New Haven, Connecticut 06520-8284, USA.
authors.initials: AA
authors.lastname: Kozhevnikov
authors.initials: RJ
authors.lastname: Schoelkopf
authors.initials: DE
authors.lastname: Prober