The XPS valence band spectra of Hf metal and HfC x N y O z compounds and the correlation to their superconductivity

The x-ray photoemission spectra of the valence bands of Hf metal and of several HfC_xN_yO_z compounds have been measured and are compared to existing band structure calculations. The density of states at the Fermi energy of the HfC_xN_yO_z compounds correlates strongly to their superconducting transition temperatureT_c. A calculation of theT_c values within the frame work of strong coupling superconductors indicates that the phonon spectrum and the electron phonon interaction is approximately constant within the series HfC_xN_yO_z.