Mass Enhancement in an Intermediate-Valent Regime of Heavy-Fermion Systems

TL;DR

This paper investigates the mechanism behind mass enhancement in heavy-fermion systems within an intermediate-valent regime, revealing sharp crossovers and significant mass increases not predicted by earlier theories, with relevance to experimental observations.

Contribution

It introduces a new theoretical understanding of mass enhancement in intermediate-valent heavy-fermion materials, highlighting the role of Coulomb interactions and sharp crossovers.

Findings

Sharp crossovers between regimes with Coulomb interaction

Substantial mass enhancement in intermediate-valent regime

Relevance to experimental observations in CeCu2Si2 and YbAlB4

Abstract

We study the mechanism of the mass enhancement in an intermediate-valent regime of heavy-fermion materials. We find that the crossovers between the Kondo, intermediate valent, and almost empty f-electron regimes become sharp with the Coulomb interaction between the conduction and f electrons. In the intermediate-valent regime, we find a substantial mass enhancement, which is not expected in previous theories. Our theory may be relevant to the observed nonmonotonic variation in the effective mass under pressure in CeCu2Si2 and the mass enhancement in the intermediate-valent compounds alpha-YbAlB4 and beta-YbAlB4.