Evolution of the Kondo state of YbRh2Si2 probed by high field ESR

TL;DR

This study uses high field ESR to investigate the evolution of the Kondo state in YbRh2Si2, revealing heavy fermion formation below T_K and how magnetic fields influence their properties and anisotropy.

Contribution

It provides new insights into the field-dependent evolution of the Kondo state and heavy fermion behavior in YbRh2Si2 through ESR measurements.

Findings

ESR signal appears below T_K indicating heavy fermion formation

ESR parameters correlate with specific heat and NMR data

Magnetic field tunes the Kondo state, affecting ESR g-factor and linewidth

Abstract

An electron spin resonance (ESR) study of the heavy fermion compound YbRh2Si2 for fields up to ~ 8 T reveals a strongly anisotropic signal below the single ion Kondo temperature T_K ~ 25 K. A remarkable similarity between the T-dependence of the ESR parameters and that of the specific heat and the 29Si nuclear magnetic resonance data gives evidence that the ESR response is given by heavy fermions which are formed below T_K and that ESR properties are determined by their field dependent mass and lifetime. The signal anisotropy, otherwise typical for Yb{3+} ions, suggests that, owing to a strong hybridization with conduction electrons at T < T_K, the magnetic anisotropy of the 4f states is absorbed in the ESR of heavy quasiparticles. Tuning the Kondo effect on the 4f states with magnetic fields ~ 2 - 8 T and temperature 2 - 25 K yields a gradual change of the ESR g-factor and linewidth which reflects the evolution of the Kondo state in this Kondo lattice system.