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 the shot noise develops features at bias voltages , 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 , due to Andreev reflection.
- Received 12 November 1999
DOI:https://doi.org/10.1103/PhysRevLett.84.3398
©2000 American Physical Society