Berlin 2008 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 19: Correlated Electrons: Quantum-Critical Phenomena
TT 19.5: Vortrag
Dienstag, 26. Februar 2008, 15:00–15:15, H 3010
Anomalous critical behavior at the antiferromagnetic phase transition of YbRh2Si2 — •Cornelius Krellner1, Stefanie Hartmann1, Adam Pikul1, Niels Oeschler1, Christoph Geibel1, Jochen Wosnitza2, and Frank Steglich1 — 1Max Planck Institute for Chemical Physics of Solids, Dresden, Germany — 2HLD, Forschungszentrum Dresden-Rossendorf, Dresden, Germany
Quantum phase transitions are one of the important topics in the understanding of condensed matter. These transitions are driven by quantum fluctuations in contrast to classical phase transitions which are accompanied by thermal fluctuations. Recently, the heavy-fermion system YbRh2Si2 was intensively studied, because it is a clean and stoichiometric metal situated on the magnetic side (TN=72 mK), but very close to a quantum critical point, which can be crossed by applying a tiny magnetic field. Therefore, this system presents both an antiferromagnetic phase transition driven by thermal fluctuations as well as pronounced quantum fluctuations due to the vicinity to the quantum phase transition. In this contribution, we show accurate measurements of the specific heat C around TN on a single crystal of highest quality (RRR ∼ 150). We observe a very sharp peak at TN with absolute values as high as C/T=8 J/mol K2. A detailed analysis of the critical exponent α around TN reveals α = 0.37 which differs significantly from those of the conventional universality classes in the Landau theory α < 0.11. We will discuss in detail the analysis and possible mechanisms.