Direct observation of Coulomb interactions in highly conducting [2,5-dimethyl-dicyanoquinonediimine]2Ag

Abstract
Valence-band photoelectron spectroscopy and scanning-tunneling microscopy demonstrate the significance of Coulomb interactions for the semiconducting state of single crystalline [2,5-dimethyl-dicyanoquinonediimine]2Ag. Direct evidence for the electron-electron interactions is deduced from the spectroscopic observation of a pseudogap in the density of states near the Fermi energy and from the dimerization in real space observed by tunneling microscopy.