Photoemission experiments on YbInCu{sub 4}: Surface effects and temperature dependence

We present temperature-dependent photoemission (PES) measurements on single-crystalline YbInCu{sub 4}, a stoichiometric material that shows an isostructural first-order valence transition at T{sub a}{approx}60 K. The results of the analysis of the PES data show peculiar differences to other, bulk-sensitive measurements: (a) a lack of the sharp first-order valence transition and (b) the Yb valence {emdash} determined directly from the 4f intensity ratio {emdash} lies substantially below x-ray absorption (XAS) results over the whole investigated temperature range. We discuss these discrepancies with particular attention to surface effects and conclude that the PES results are due to a distorted near-surface region which differs in its physical properties significantly from the volume material. {copyright} {ital 1998} {ital The American Physical Society}