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Phys Rev Lett. 2003 Aug 8;91(6):066405. Epub 2003 Aug 5.

Divergence of the grüneisen ratio at quantum critical points in heavy fermion metals.

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1
Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.

Abstract

We present low-temperature volume thermal expansion, beta, and specific heat, C, measurements on high-quality single crystals of CeNi2Ge2 and YbRh2(Si0.95Ge0.05)(2) which are located very near to quantum critical points. For both systems, beta shows a more singular temperature dependence than C, and thus the Grüneisen ratio Gamma proportional to beta/C diverges as T-->0. For CeNi2Ge2, our results are in accordance with the spin-density wave (SDW) scenario for three-dimensional critical spin fluctuations. By contrast, the observed singularity in YbRh2(Si0.95Ge0.05)(2) cannot be explained by the itinerant SDW theory but is qualitatively consistent with a locally quantum critical picture.

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