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

ABSTRACT

In 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 YbNi${}_3$Ga${}_9$ and EuFe${}_2$As${}_2$, revealing the characteristic pressure-induced valence crossover and possibly the relevance of the valence instability to the physical properties near the magnetic QCP.

KEYWORDS:

• Quantum phase transition
• high pressure
• X-ray absorption spectroscopy
• heavy fermion
• valence

Acknowledgments

We acknowledge discussions with S. Watanabe, K. Miyake, N. K. Sato, S. Ohara, K. Ohgushi and Y. Uwatoko. We are grateful to H. Sumiya and T. Irifune for providing the NPD anvils.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work is partially supported by Grants-in-Aid (No. 24740220 and No. 24540389) for Scientific Research from the Japan Society for the Promotion of Science, the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (Proposals No. 2011B2097, No. 2011B2094, No. 2011B2092, No. 2012A1283, No. 2012A1843, No. 2012B1976, No. 2012B1978, No. 2012B0046, No. 2013A0046), and Grants-in-Aid for Scientific Research on Innovative Areas Heavy Electrons (No. 20102007) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.