Bose-Einstein Condensation of Magnons in TlCuCl3: Phase diagram and specific heat from a self-consistent Hartee-Fock calculation with a realistic dispersion relation

TL;DR

This paper models the Bose-Einstein condensation of magnons in TlCuCl3 using an advanced Hartree-Fock approach with realistic dispersion, accurately predicting critical fields and specific heat behavior that align with experimental data.

Contribution

It introduces a realistic dispersion relation into the self-consistent Hartree-Fock-Popov calculations for magnon BEC in TlCuCl3, improving agreement with experiments.

Findings

Critical field Hc(T) follows T^{3/2} law below 2K

Specific heat exhibits a lambda-like transition at the critical point

Model results agree well with experimental measurements of phase diagram and specific heat

Abstract

We extend the self-consistent Hartree-Fock-Popov calculations by Nikuni et al. [Phys. Rev. Lett. 84, 5868 (2000)] concerning the Bose-Eistein condensation of magnons in TlCuCl3 to include a realistic dispersion of the excitations. The result for the critical field as a function of temperature behaves as Hc(T)-Hc(0) T^{3/2} below 2K but deviates from this simple power-law at higher temperature and is in very good agreement with the experimental results. The specific heat is computed as a function of temperature for different values of the magnetic field. It shows a lambda-like shape at the transition and is in good qualitative agreement with the results of Oosawa et al. [Phys. Rev. B 63, 134416 (2001)].