XPS and UPS Studies of Valence Fluctuation and Surface States of Yb₄As₃, Yb₄Sb₃ and Yb₄Bi₃

Abstract

X-ray and vacuum ultraviolet photoemission spectra were measured for valence fluctuating Yb₄X₃ (X: As, Sb and Bi) by use of Mg K_α and synchrotron radiation source. From the line shape analysis of the Yb 4f spectra, the mean valence is evaluated as 2.32, 2.34 and 2.10 for Yb₄As₃,Yb₄Sb₃ and Yb₄Bi₃. The surface Yb 4f level shift is estimated as 0.65, 0.63 and 0.59 eV, respectively. The plasmon satellite is confirmed in the Yb 4f and Yb 4d core XPS spectra of Yb₄Bi₃ in contrast to those in Yb₄As₃ and YbAs. As for the anionic states, the Bi 5d core UPS spectrum showed a remarkable asymmetry in contrast to the rather symmetric Bi 4f core XPS spectrum. This result suggests a contribution of the surface Bi 5d state at larger binding energies of about 0.5 eV.