Gr\"uneisen ratio at the Kondo breakdown quantum critical point

TL;DR

This paper demonstrates that the multi-scale Kondo breakdown quantum critical point causes a divergent Gr"uneisen ratio with an anomalous exponent, aligning well with experimental data and aiding in distinguishing theoretical models.

Contribution

It provides a simple analytic framework linking the Kondo breakdown QCP to the Gr"uneisen ratio and compares it with experimental results for the first time.

Findings

Gr"uneisen ratio diverges with an exponent of 0.7 at the QCP.

Analytic expressions fit experimental data between 0.4 K and 10 K.

Gr"uneisen ratio can differentiate between Kondo breakdown and spin-density wave theories.

Abstract

We show that the scenario of multi-scale Kondo breakdown quantum critical point (QCP) gives rise to a divergent Gr\"uneisen ratio with an anomalous exponent 0.7. In particular, we fit the experimental data of $YbRh_{2}(Si_{0.95}Ge_{0.05})_{2}$ for specific heat, thermal expansion, and Gr\"uneisen ratio based on our simple analytic expressions. A reasonable agreement between the experiment and theory is found for the temperature range between 0.4 K and 10 K. We discuss how the Gr\"uneisen ratio is a key measurement to discriminate between the Kondo breakdown and spin-density wave theories.