Violation of critical universality at the antiferromagnetic phase transition of YbRh2Si2

TL;DR

This study presents precise low-temperature specific-heat measurements of YbRh2Si2 near its antiferromagnetic transition, revealing a critical exponent that challenges conventional universality classes and offers insights into quantum critical fluctuations.

Contribution

The paper provides the first detailed critical exponent analysis at the antiferromagnetic transition of YbRh2Si2, showing violation of expected universality classes.

Findings

Critical exponent =0.38 significantly exceeds conventional values.

Sharp peak in specific heat at T_N=72mK indicates a well-defined phase transition.

Thermal expansion measurements support the large positive critical exponent.

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 (RRR 150). We observe a very sharp peak at T_N=72mK with absolute values as high as C/T=8J/molK^2. 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<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.