Temperature dependence of the Yb 4f spectra in Yb4Bi3 probed by photoemission spectroscopy

We have performed a photoemission study of Yb4Bi3. The valence band spectra have shown no multiplet structures associated with the trivalent Yb and re vealed that the mean valence of the Yb ion is very close to 2.0. The divale nt Yb 4f spectra have shown strong surface components besides weak but shar p bulk components. The surface 4f level shift is about 0.45 eV (300 K), 0.4 8 eV (150 K) and 0.54 eV (20 K). A clear energy shift of the bulk Yb If pea ks toward EF with decreasing temperature has been observed, although Yb4Bi3 shows neither phase transition nor crossover. Such an unusual peak shift o f the bulk component may originate from a change of the lattice constant wi th decreasing temperature. The observed narrowing or the bulk 4f peaks is t hought to be due to a phonon broadening (similar to 7 k(B)T).