TEMPERATURE-DEPENDENCE OF 4F PES FEATURES AND HOLE OCCUPANCY IN YTTERBIUM HEAVY FERMIONS

We have measured the temperature dependence between 80 and 300 K and s pectral weight of the 4f features in clean single crystal Yb heavy fer mions, cleaved in a vacuum of 5 x 10(-11) Torr. A small (approximately 15%) decrease in spectral weight differs substantially from the repor ted approximately 50% decrease over this range. All divalent features are much larger than expected, yielding nf values far too small. The i ntensity of the divalent features in YbAuCu4 is about two orders of ma gnitude larger than expected.