Reply to “Comment on ‘Photoemission experiments on YbInCu 4 : Surface effects and temperature dependence’ ”

The stoichiometric rare-earth compound ${\mathrm{YbInCu}}_{4}$ is known for its first-order valence transition at ${T}_{a}\ensuremath{\approx}55\mathrm{K}$ and ambient pressure. Although this valence transition has been extensively studied by various volume-sensitive experimental methods, highly surface-sensitive photoemission measurements in the vuv energy range [ultraviolet photoemission spectroscopy (UPS)] could not observe a sharp valence change of the Yb valence ${v}_{\mathrm{Yb}}$ at the transition temperature. Instead there is only a smooth temperature dependence of ${v}_{\mathrm{Yb}}$ over a large temperature range. Furthermore, the low-temperature values for the hole-occupation number ${n}_{h}{=v}_{\mathrm{Yb}}\ensuremath{-}2$ from UPS are significantly below the values of volume-sensitive measurements. Here we present temperature-dependent photoemission data on ${\mathrm{YbInCu}}_{4}$ measured at photon energies of $h\ensuremath{\nu}=1486\mathrm{eV}$ [x-ray photoemission spectroscopy (XPS)] with a significantly increased information depth in comparison to previous experiments with lower photon energies. These data clearly show the existence of a valence transition at the extended sampling depth of the XPS experiment, in contrast to results from the distorted near-surface region.