Divergent Thermal Expansion and Gr\"uneisen Ratio in a Quadrupolar Kondo Metal

TL;DR

This study investigates the low-temperature thermal expansion and magnetostriction in a quadrupolar Kondo metal, revealing singular behaviors and divergences consistent with Kondo effects and suggesting complex elastic interactions.

Contribution

It provides the first detailed measurements of thermal expansion and magnetostriction in a quadrupolar Kondo candidate, highlighting singular strain behaviors linked to Kondo correlations.

Findings

Quadrupolar strain shows a $H^2 \, \log 1/T$ dependence.

The quadrupolar Gr"uneisen ratio diverges as $H^2/(T^2 \log 1/T)$.

Zero-field isotropic strain exhibits divergence, indicating complex elastic effects.

Abstract

We report on the low-temperature thermal expansion and magnetostriction of the single-impurity quadrupolar Kondo candidate Y$_{1-x}$Pr$_{x}$Ir$_2$Zn$_{20}$. In the dilute limit, we find a quadrupolar strain that possesses a singular dependence on temperature $T$, $\varepsilon_{\mathrm{u}} \sim H^2 \log 1/T$, for a small but finite magnetic field $H$. Together with the previously reported anomalous specific heat $C$, this implies a quadrupolar Gr\"uneisen ratio $\Gamma_u = \partial_T \varepsilon_{\mathrm{u}}/C \sim H^2/(T^2 \log 1/T)$ whose divergence for finite $H$ is consistent with the scenario of a quadrupolar Kondo effect. In addition, we find a singular behavior of the isotropic strain $\varepsilon_{\mathrm{B}}$ in zero magnetic field resulting in a divergence of both the volume thermal expansion and the volume Gr\"uneisen parameter. We speculate that this behavior might be also induced by putative Kondo correlations via elastic anharmonicities or static strain disorder.