Grueneisen Ratio Divergence at the Quantum Critical Point in CeCu_{6-x}Ag_x

TL;DR

This study investigates the quantum critical behavior of CeCu_{6-x}Ag_x, revealing that the divergence of the Grüneisen ratio at the critical point does not follow the predictions of the itinerant SDW theory, indicating a different underlying quantum critical mechanism.

Contribution

The paper provides experimental evidence that the Grüneisen ratio divergence at the quantum critical point in CeCu_{6-x}Ag_x deviates from SDW theory predictions, suggesting alternative quantum critical behavior.

Findings

Grüneisen ratio diverges weaker than SDW theory predicts

Specific heat and thermal expansion resemble YbRh2(Si0.95Ge0.05)2 behavior

Results challenge the applicability of itinerant SDW theory to this system

Abstract

The heavy fermion system CeCu$_{6-x}$Ag$_x$ is studied at its antiferromagnetic quantum critical point, $x_c=0.2$, by low temperature ($T\geq 50$ mK) specific heat, $C(T)$, and volume thermal expansion, $\beta(T)$, measurements. Whereas $C/T\propto \log(T_0/T)$ would be compatible with the predictions of the itinerant spin-density-wave (SDW) theory for two-dimensional critical spin fluctuations, $\beta(T)/T$ and the Gr\"uneisen ratio, $\Gamma(T)\propto \beta/C$, diverge much weaker than expected, in strong contrast to this model. Both $C$ and $\beta$, plotted as a function of the reduced temperature $t=T/T_0$ with $T_0=4.6$ K are similar to what was observed for YbRh$_2$(Si$_{0.95}$Ge$_{0.05}$)$_2$ ($T_0=23.3$ K) indicating a striking discrepancy to the SDW prediction in both systems.