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