Disappearance of hyperscaling at low temperatures in non-Fermi-liquid CeCu5.2Ag0.8

Following the recently published results (down to 0.3 K) on magnetic-field induced non-Fermi-liquid behavior in polycrystalline CeCu6-xAgx (0.09<x<1.2) we present here specific heat C measurements down to T=70 mK on a CeCu5.2Ag0.8 Single crystal. In the single crystal we find that in a critical magnetic field B-c only along the magnetic easy (c) axis, where the long-range antiferromagnetic order (T-N= 0.7 K in B = 0 T) is just suppressed to T=0, a quantum critical point is reached with non-Fermi-liquid properties down to our lowest temperature of measurement. The lowest temperature CIT data, B parallel to c, for B>B-c are proportional to 1 -aT(0.5), a temperature dependence proposed in the Gaussian (double left right arrow weakly interacting spin fluctuations) self-consistent renormalized spin-fluctuation theory. In contrast, the data at higher temperatures-including scaling with B/T-beta of both C and magnetization as a function of B-require a non-Gaussian strongly interacting spin-fluctuation model. In order to test this apparent crossover in behavior we have examined the scaling of C(B) for T<0.2 K and find that the high-temperature scaling with B/T-beta ("hyperscaling") does not function at the lowest temperatures. [S0163-1829(98)51648-7].