Unoccupied Electronic State of Delafossite-Type PdCoO2Single Crystal Probed Using Inverse Photoemission Spectroscopy

The unoccupied electronic state of delafossite-type PdCoO 2 has been studied using inverse-photoemission spectroscopy (IPES). The Fermi edge and the unoccupied density-of-state (DOS) at the Fermi level ( E F ) are not observed in the IPES spectrum measured at the incidence electron energy ( E K ) of 100 eV, which corresponds to the Cooper minimum of Pd 4 d . The finite DOS at E F is observed in the IPES spectra measured at the lower E K , which the ionization cross section of Pd 4 d increases. These findings indicate that the Pd 4 d electron is closely related to the low electrical resistivity of PdCoO 2 .