Strongly reduced band gap in a correlated insulator in close proximity to a metal

Abstract

Using a combination of photoelectron and inverse photoelectron spectroscopy, we show that the band gap in a monolayer of C₆₀ on a Ag surface is strongly reduced from the solid C₆₀ surface value. We argue that this is a result of the reduction of the on-site molecular Coulomb interaction due to the influence of image charges in the metal substrate. This result suggests that the physical properties of correlated insulators and semiconductors will be strongly modified if prepared in ultra thin form on metal substrates or sandwiched between metal layers.