Photon-assisted tunneling in normal-metal point contacts

Abstract
It is shown experimentally that the response of normal-metal point contacts at low temperatures to radiation starts to deviate from classical detection when the frequency approaches the Debye frequency. The high-frequency response can be described with the photon-assisted tunneling (PAT) theory. This implies the first observation of the PAT effect in a nonlinear element where no superconductor is involved.