Quantum Griffiths phase in the kagome Kondo lattice CeRh$_{0.9}$Pd$_{0.1}$Sn

TL;DR

This study investigates the quantum Griffiths phase in a kagome lattice heavy-fermion metal, revealing non-Fermi liquid behavior and disorder-driven quantum criticality without conventional quantum critical signatures.

Contribution

It provides experimental evidence for a quantum Griffiths phase in CeRh$_{0.9}$Pd$_{0.1}$Sn, expanding understanding of disorder effects in quantum critical systems.

Findings

Absence of Gr"uneisen parameter divergence rules out conventional quantum criticality.

Weak power-law divergences indicate non-Fermi liquid behavior.

Negative thermal expansion observed above 0.5 T in magnetic field.

Abstract

CeRhSn is a valence fluctuating heavy-fermion metal with a twisted Ce-kagome lattice, displaying zero-field quantum criticality, previously associated with geometrical frustration. The partial substitution of Rh by Pd in CeRh$_{1-x}$Pd$_x$Sn enlarges the unit-cell volume, suppresses valence fluctuations, decreases the Kondo temperature and stabilizes a possible long-range antiferromagnetic (AFM) ordered ground state with $T_N=0.8$ K at $x=0.5$. Previous thermodynamic and spectroscopic measurements for $x=0.1$ suggested a quantum critical spin liquid. We report low-temperature dilatometry and magnetization measurements on CeRh$_{0.9}$Pd$_{0.1}$Sn and compare with published low-$T$ specific heat data. The absence of a Gr\"uneisen parameter divergence excludes a conventional quantum criticality scenario. Instead, the weak power-law divergences signal non-Fermi liquid (NFL) behavior, according to a disorder-driven quantum Griffiths phase scenario. At low temperatures, a negative thermal expansion is found in fields above approximately 0.5 T and the NFL scaling breaks down, probably due to the polarization of AFM correlations.