Pressure-induced valence change toward the QCP in 4f-electron compounds determined by X-ray absorption spectroscopy

Abstract

ABSTRACTIn strongly correlated electron systems, a fundamental understanding of the quantum critical behavior in the vicinity of a magnetic quantum critical point (QCP) remains one of the important issues for decades. In particular, the unconventional criticality, which cannot be explained by the spin fluctuation theory, has attracted much attention in 4f electron systems, and the role of the valence instability has been discussed both from theoretical and experimental points of view. Here, we present our systematic high pressure study of X-ray absorption spectra on YbNiGa and EuFeAs, revealing the characteristic pressure-induced valence crossover and possibly the relevance of the valence instability to the physical properties near the magnetic QCP.