Behavior of the antiferromagnetic phase transition near the fermion condensation quantum phase transition in YbRh2Si2

TL;DR

This paper investigates the antiferromagnetic phase transition in YbRh2Si2 near a fermion condensation quantum critical point, revealing a change from second to first order transition and explaining critical exponents with Landau theory.

Contribution

It demonstrates how fermion condensation quantum phase transition influences the nature of the antiferromagnetic phase transition and explains the observed critical exponents.

Findings

Critical exponent alpha=0.38 differs from fluctuation theory prediction.

Transition changes from second to first order at the tricritical point under magnetic field.

Landau theory accurately describes the critical behavior near the tricritical point.

Abstract

Low-temperature specific-heat measurements on YbRh2Si2 at the second order antiferromagnetic (AF) phase transition reveal a sharp peak at T_N=72 mK. The corresponding critical exponent alpha turns out to be alpha=0.38, which differs significantly from that obtained within the framework of the fluctuation theory of second order phase transitions based on the scale invariance, where alpha=0.1. We show that under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point leading to a violation of the critical universality of the fluctuation theory. This change of the phase transition is generated by the fermion condensation quantum phase transition. Near the tricritical point the Landau theory of second order phase transitions is applicable and gives alpha=1/2. We demonstrate that this value of alpha is in good agreement with the specific-heat measurements.