Temperature and Pressure Dependences of the Electronic and Crystal Structures of Yb4TGe8 (T = Cr, Mn, Fe, Co, and Ni) Studied by High-resolution X-ray Absorption Spectroscopy, X-ray Diffraction, and Photoelectron Spectroscopy

Abstract

Temperature and pressure dependences of the electronic structure of the Kondo lattice systems of Yb4CrGe8 and Yb4MnGe8 have been investigated in detail using high-resolution x-ray absorption spectroscopy. Temperature-induced valence changes of Yb are on the order of 0.08 for Yb4MnGe8 and 0.1 for Yb4CrGe8 at the temperature range between 12 and 300 K. The c–f hybridization remains at the low temperatures where the crossover from Fermi liquid to non-Fermi liquid like behavior occurs. We also measured the x-ray absorption spectra of Yb4CrGe8 at the Cr-K and Ge-K absorption edges and found the hybridization of 3d orbitals of Cr with the Yb band at low temperatures. Photoelectron spectroscopy of Yb4TGe8 (T = Cr, Mn, Fe, Co, and Ni) showed an anomaly of the energy shift of the Yb3+ component in the valence band spectra. The Yb valence increased rapidly with pressure up to 6–7 GPa, and further increase in the pressure did not change the Yb valence significantly. The compressibility along the b axis is larger than those along the a and c axes.