title: Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2.
abstract: We report on precise low-temperature specific-heat measurements, C(T), of YbRh2Si2 in the vicinity of the antiferromagnetic phase transition on a single crystal of superior quality (residual resistivity ratio of approximately 150). We observe a very sharp peak at T_{N}=72 mK with absolute values as high as C/T=8 J/mol K2. A detailed analysis of the critical exponent alpha around T_{N} reveals alpha=0.38 which differs significantly from those of the conventional universality classes in the Ginzburg-Landau theory, where alpha< or =0.11. Thermal-expansion measurements corroborate this large positive critical exponent. These results provide insight into the nature of the critical magnetic fluctuations at a temperature-driven phase transition close to a quantum critical point.
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany. krellner@cpfs.mpg.de
authors.forename: C
authors.initials: C
authors.lastname: Krellner
authors.forename: S
authors.initials: S
authors.lastname: Hartmann
authors.forename: A
authors.initials: A
authors.lastname: Pikul
authors.forename: N
authors.initials: N
authors.lastname: Oeschler
authors.forename: J G
authors.initials: JG
authors.lastname: Donath
authors.forename: C
authors.initials: C
authors.lastname: Geibel
authors.forename: F
authors.initials: F
authors.lastname: Steglich
authors.forename: J
authors.initials: J
authors.lastname: Wosnitza