Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2.
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.
Krellner
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C
Max Planck Institute for Chemical Physics of Solids, D-01187 Dresden, Germany. krellner@cpfs.mpg.de
Hartmann
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S
Pikul
A
A
Oeschler
N
N
Donath
J G
JG
Geibel
C
C
Steglich
F
F
Wosnitza
J
J