Valence Transition of YbInCu4 Observed by Photoemission Spectroscopy

Abstract

First-order valence transition of YbInCu4 at TV=42 K has directly been observed by photoemission spectroscopy (PES) using wide excitation photon energies from extremely low-energy region (hν=7 eV) to soft x-ray region (hν=800 eV), and further to hard x-ray region (hν=6 keV). The valence transition is more sharply observed in the hard x-ray PES spectra than the soft x-ray PES spectra. We demonstrate that the Yb 3d hard x-ray PES is very suitable for the estimation of the Yb valences with high accuracy, and they have been derived to be ∼2.90 in the high-temperature phase and ∼2.74 in the low-temperature phase. In the low-energy PES spectra, on the other hand, the hybridization band between the conduction-band (CB) and Yb 4f states is observed as a remarkable structure at 47 meV below the Fermi level. This structure suddenly appears below TV, indicating that a degree of the c-f hybridization increases in the low-temperature phase. [DOI: 10.1380/ejssnt.2011.90]