Roles of Critical Valence Fluctuations in Ce- and Yb-Based Heavy Fermion Metals

TL;DR

This paper explores how critical valence fluctuations influence anomalies in Ce- and Yb-based heavy fermion metals, highlighting the role of magnetic fields in controlling valence transitions and their impact on magnetic and electronic properties.

Contribution

It introduces a theory showing magnetic fields can induce critical valence fluctuations, unifying understanding of various phenomena in heavy fermion systems.

Findings

Magnetic field induces critical end point of valence transition.

Suppression of magnetic order by valence fluctuations explains CeRhIn5 behavior.

Broader applicability to materials like YbAuCu4 and YbRh2Si2.

Abstract

The roles of critical valence fluctuations of Ce and Yb are discussed as a key origin of several anomalies observed in Ce- and Yb-based heavy fermion systems. Recent development of the theory has revealed that a magnetic field is an efficient control parameter to induce the critical end point of the first-order valence transition. Metamagnetism and non-Fermi liquid behavior caused by this mechanism are discussed by comparing favorably with CeIrIn5, YbAgCu4, and YbIr2Zn20. The interplay of the magnetic order and valence fluctuations offers a key concept for understanding Ce- and Yb-based systems. It is shown that suppression of the magnetic order by enhanced valence fluctuations gives rise to the coincidence of the magnetic-transition point and valence-crossover point at absolute zero as a function of pressure or magnetic field. The interplay is shown to resolve the outstanding puzzle in CeRhIn5 in a unified way. The broader applicability of this newly clarified mechanism is discussed by surveying promising materials such as YbAuCu4, beta-YbAlB4, and YbRh2Si2.