Unoccupied electronic state of delafossite-type PdCoO2 single crystal probed using inverse photoemission spectroscopy

The unoccupied electronic state of delafossite-type PdCoO2 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 100eV, which corresponds to the Cooper minimum of Pd 4d. 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 4d increases. These findings indicate that the Pd 4d electron is closely related to the low electrical resistivity of PdCoO2.