Anomalous critical behavior at the antiferromagnetic phase of YbRh₂Si₂

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/molK2. 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 mechanism.