Thermal expansion in photo-assisted tunneling: Visible light versus free-space terahertz pulses

Abstract

Photo-assisted tunneling in scanning tunneling microscopy has attracted considerable interest to combine sub-picosecond and sub-nanometer resolutions. The illumination of a junction with visible or infrared light, however, induces thermal expansion of the tip and the sample, which strongly affects the measurements. Employing free-space THz pulses instead of visible light has been proposed to solve these thermal issues while providing photo-induced currents of similar magnitude. Here we compared the impact of illuminating the same tunneling junction, reaching comparable response in the tunneling current, with red light and with THz radiations. Our data provide a clear and direct evidence of thermal expansion with red light-illumination, while such thermal effects are negligible with THz radiations.