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

R. Kuechler; P. Gegenwart; K. Heuser; E. -W. Scheidt; G. R. Stewart; F. Steglich

doi:10.1103/PhysRevLett.93.096402

paper

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

arXiv:cond-mat/0407798 · doi:10.1103/PhysRevLett.93.096402

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, $β (T)$ , measurements. Whereas $C / T \propto lo g (T_{0} / T)$ would be compatible with the predictions of the itinerant spin-density-wave (SDW) theory for two-dimensional critical spin fluctuations, $β (T) / T$ and the Grüneisen ratio, $Γ (T) \propto β / C$ , diverge much weaker than expected, in strong contrast to this model. Both $C$ and $β$ , 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.

Physical Review Letters, to be published