Conduction-band electronic states of YbInCu4studied by photoemission and soft x-ray absorption spectroscopies

Abstract

We have studied conduction-band (CB) electronic states of a typical valence-transition compound YbInCu${}_{4}$ by means of temperature-dependent hard x-ray photoemission spectroscopy (HX-PES) of the Cu 2$p$${}_{3/2}$ and In 3$d$${}_{5/2}$ core states taken at $h\ensuremath{\nu}=5.95$ keV, soft x-ray absorption spectroscopy (XAS) of the Cu 2$p$${}_{3/2}$ core absorption region around $h\ensuremath{\nu}\ensuremath{\sim}935$ eV, and soft x-ray photoemission spectroscopy (SX-PES) of the valence band at the Cu 2$p$${}_{3/2}$ absorption edge of $h\ensuremath{\nu}=933.0$ eV. With decreasing temperature below the valence transition at ${T}_{V}=42$ K, we have found that (1) the Cu 2$p$${}_{3/2}$ and In 3$d$${}_{5/2}$ peaks in the HX-PES spectra exhibit the energy shift toward the lower binding-energy side by $\ensuremath{\sim}$40 and $\ensuremath{\sim}$30 meV, respectively, (2) an energy position of the Cu 2$p$${}_{3/2}$ main absorption peak in the XAS spectrum is shifted toward higher photon-energy side by $\ensuremath{\sim}$100 meV, with an appearance of a shoulder structure below the Cu 2$p$${}_{3/2}$ main absorption peak, and (3) an intensity of the Cu $L$${}_{3}$$VV$ Auger spectrum is abruptly enhanced. These experimental results suggest that the Fermi level of the CB-derived density of states is shifted toward the lower binding-energy side. We have described the valence transition in YbInCu${}_{4}$ in terms of the charge transfer from the CB to Yb 4$f$ states.