Role of optical rectification in photon-assisted tunneling current

Emission of light and conversely rectification of an optical signal using an all-metallic electronic device is of fundamental and technological importance for nano-optics. However despite recent experimental efforts in the development of electrically-driven plasmonic sources, the interplay between quantum transport and optics is still under debate. Here, we measure the photon-assisted current in a planar tunnel junction under infrared illumination. To address the microscopic mechanism at the origin of the optical rectification, we compare the photon-assisted current and the current-voltage characteristic of the junction measured on a voltage range much greater than V_0=hc/eλ=0.825 V , previously unexplored. The experimental results do not agree with the theory based on the existence of a non-thermal distribution function corresponding to the exchange of energy quanta between electrons and photons. We show instead that the illumination power mainly goes into heating and that the rectification results from the tunneling Seebeck effect.