Schematic of the density of electronic states (top) where the Coulomb energy U and charge transfer energy are indicated. Typical measured differential conductance g ( V ) spectrum (bottom) where the top of the lower band and the bottom of the upper band are visualized, their separation being a direct measure of charge transfer energy (ref. 25 ). CTB represents the charge transfer band, LHB represents the lower Hubbard band and UHB represents the upper Hubbard band.
