Insight on the interaction between image potential state and π bands in graphite

We demonstrate that the electron density of the light-populated image potential states in graphite reaches its maximum when the photon energy of ultrashort laser pulses is resonant with the π−π* band gap at the M point of the Brillouin zone. This unexpected behavior, as shown by the nonlinear photoelectron spectroscopy data, is assisted by the onset of a strong light-induced interaction between the π bands and the image potential states. This finding suggests the possibility of exploring new photochemical processes at the graphite surface and related compounds.