title: Divergence of the grüneisen ratio at quantum critical points in heavy fermion metals.
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.
authors.affiliation: Max-Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Küchler
authors.forename: N
authors.initials: N
authors.lastname: Oeschler
authors.forename: P
authors.initials: P
authors.lastname: Gegenwart
authors.forename: T
authors.initials: T
authors.lastname: Cichorek
authors.forename: K
authors.initials: K
authors.lastname: Neumaier
authors.forename: O
authors.initials: O
authors.lastname: Tegus
authors.forename: C
authors.initials: C
authors.lastname: Geibel
authors.forename: J A
authors.initials: JA
authors.lastname: Mydosh
authors.forename: F
authors.initials: F
authors.lastname: Steglich
authors.forename: L
authors.initials: L
authors.lastname: Zhu
authors.forename: Q
authors.initials: Q
authors.lastname: Si