Suppression of f-Electron Itinerancy in CeRu2Si2 by a Strong Magnetic Field

TL;DR

This study investigates how strong magnetic fields suppress the itinerant nature of 4f electrons in CeRu2Si2, revealing gradual valence reduction and insights into the breakdown of the Kondo state under high magnetic fields.

Contribution

It provides the first detailed measurement of valence changes in CeRu2Si2 under high magnetic fields, linking electron localization to metamagnetic behavior.

Findings

Valence slightly above Ce3+ at zero field

Valence decreases with increasing magnetic field

Itinerant character persists up to 40 T, suggesting gradual Kondo breakdown

Abstract

The valence state of Ce in a canonical heavy fermion compound CeRu2Si2 has been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high magnetic fields of up to 40 T. The valence was slightly larger than for the pure trivalent state (Ce3+: f1), as expected in heavy fermion compounds, and it decreased toward the trivalent state as the magnetic field was increased. The field-induced valence reduction indicates that the itinerant character of the 4f electrons in CeRu2Si2 was suppressed by a strong magnetic field. The suppression was gradual and showed characteristic magnetic field dependence, which reflects the metamagnetism around Hm \sim 8 T. The itinerant character persisted, even at 40 T (\sim 5Hm), suggesting that the Kondo bound state is continuously broken by magnetic fields and that it should completely collapse at fields exceeding 200 T.