Band-edge detection in insulators by tunneling spectroscopy

Abstract

Tunneling spectroscopy on a thin metal film, having a thickness less than a conduction-electron mean free path, can reveal band-structure features of an insulating substrate upon which the film has been overlaid. Virtual transitions which couple energy-band states of the substrate with conduction-band states of the metal create subsidiary structure in the metal’s density of states. It is shown that band edges of the insulator should cause sharp peaks in the (differential) tunneling conductance (versus bias voltage) between the metal and, for example, the tip of a scanning tunneling microscope.