Possible observation of the direct emission of radiation from tunnel junctions

Abstract
Light emission from tunnel junctions occurs when the tunnelling electrons excite surface plasmon polaritons (SPPS) and these SPPS decay by photon emission. Laks and Mills (1979, 1980) predicted an additional direct process in which optical frequency fluctuations in the tunnel current couple directly to the radiation field. The authors have observed an anomalous component in the light output from a nominally smooth aluminium-aluminium oxide-gold tunnel junction which has many of the features expected in direct emission.