STRONGLY REDUCED BAND-GAP IN A CORRELATED INSULATOR IN CLOSE PROXIMITY TO A METAL

Using a combination of photoelectron and inverse photoelectron spectro scopy, we show that the band gap in a monolayer of C-60 on a Ag surfac e is strongly reduced from the solid C-60 surface value. We argue that this is a result of the reduction of the on-site molecular Coulomb in teraction due to the influence of image charges in the metal substrate . This result suggests that the physical properties of correlated insu lators and semiconductors will be strongly modified if prepared in ult ra thin form on metal substrates or sandwiched between metal layers.