Enhancement of the effective mass at high magnetic fields in CeRhIn$_5$

TL;DR

This study investigates how high magnetic fields induce Fermi surface changes in CeRhIn$_5$, revealing enhanced effective masses and electron itineracy, with implications for understanding Kondo lattice behavior under strong magnetic fields.

Contribution

It provides new insights into the field-induced delocalization of $4f$ electrons and the robustness of Kondo coupling in CeRhIn$_5$ through comprehensive thermodynamic and quantum oscillation measurements.

Findings

Significant enhancement of Sommerfeld coefficient above 17 T

Observation of increased spin-dependent effective masses

Detection of Fermi surface reconstruction at 30 T

Abstract

The Kondo-lattice compound CeRhIn$_5$ displays a field-induced Fermi surface reconstruction at $B^*\approx30$ T, which occurs within the antiferromagnetic state, prior to the quantum critical point at $B_{c0}\approx50$ T. Here, in order to investigate the nature of the Fermi surface change, we measured the magnetostriction, specific heat, and magnetic torque of CeRhIn$_5$ across a wide range of magnetic fields. Our observations uncover the field-induced itineracy of the $4f$ electrons, where above $B_{\rm onset}\approx17$ T there is a significant enhancement of the Sommerfeld coefficient, and spin-dependent effective cyclotron masses determined from quantum oscillations. Upon crossing $B_{\rm onset}$, the temperature dependence of the specific heat also shows distinctly different behavior from that at low fields. Our results indicate that the Kondo coupling is remarkably robust upon increasing the magnetic field. This is ascribed to the delocalization of the $4f$ electrons at the Fermi surface reconstruction at $B^*$.