Temperature-dependent angular resolved UV-photoemission spectroscopy from CeNi2Ge2

Pronounced temperature effects in angular resolved ultraviolet photoelectron spectroscopy from the (001) surface of the ternary heavy fermion compound CeNi2Ge2 are presented. The measurements were performed on atomically clean and well-ordered thin films grown on a W(110) substrate. A strongly enhanced intensity at the Fermi edge (E-F) is observed at low-temperatures if the spectra are excited by means of HeI light (hv=21.2 eV). In addition, the work function is dramatically increased with temperature, exhibiting an unusually high positive temperature coefficient of about 0.65 meV/K. The observed temperature dependency suggests a strong redistribution of the states near the Fermi-energy with increasing temperature. A simple model will be given that correlates the observed intensity changes at E-F with the change of the work function. (C) 2001 Elsevier Science B.V. All rights reserved.