Gruneisen ratio divergence at the quantum critical point in CeCu6-xAgx -: art. no. 096402

The heavy-fermion system CeCu6-xAgx is studied at its antiferromagnetic quantum critical point, x(c)=0.2, by low-temperature (Tgreater than or equal to50 mK) specific heat, C(T), and volume thermal expansion, beta(T), measurements. Whereas C/Tproportional tolog(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 Gruneisen ratio, Gamma(T)proportional tobeta/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 YbRh2(Si0.95Ge0.05)(2) (T-0=23.3 K), indicating a striking discrepancy to the SDW prediction in both systems.