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In heavy-fermion systems with 4f or 5f atoms (such as Ce or U) the competition between the on-site moment compensation by the Kondo effect and the long-range RKKY interaction between localized magnetic moments leads to the possibility of either a non-magnetic or a magnetically ordered ground state. However, even in the case of no long-range magnetic order as exemplified by , short-range dynamic intersite correlations are observed. Yet, the thermodynamic and transport properties of this alloy at very low temperatures T resemble those of a Fermi liquid (FL). Upon alloying with Au, long-range incommensurate antiferromagnetism is observed in for x > 0.1. For x = 0.1 where , the specific heat C depends on T as , the magnetic susceptibility as , and the T-dependent part of the electrical resistivity as . This is in marked contrast to the FL behaviour . It is suggested that low-energy spin excitations are at the origin of these non-Fermi-liquid (NFL) anomalies which occur at a zero-temperature quantum phase transition. Large magnetic fields B restore FL behaviour. The low-T range of FL behaviour in C and extends towards higher T with increasing B, with the crossover temperature varying roughly linearly with B. Apart from changing the Au concentration x, the magnetic - non-magnetic transition can be tuned by applying pressure p to antiferromagnetic samples with x > 0.1. For x = 0.3, at and NFL behaviour is observed in the specific heat for this critical pressure. For x = 0.2, where we likewise observe a logarithmic divergence of C/T and for p = 6.9 kbar we recover FL behaviour. Finally, we report on a remarkable `universality' of C/T in the system with M = Au, Pd, Pt: regardless of how is reached in this system (alloying with different elements M, varying concentration, or applying pressure), the C/T versus ln T curves are practically identical. Possible origins of NFL behaviour are discussed.
H. v. Löhneysen (Mon,) studied this question.