Defining a critical temperature of a crossover from BEC to the normal phase in anisotropic quantum magnets

TL;DR

This paper investigates the critical temperature of the crossover from Bose-Einstein condensation to the normal phase in anisotropic quantum magnets by analyzing magnetization fluctuations and heat capacity behavior.

Contribution

It introduces a method to identify the critical temperature using magnetization fluctuations and heat capacity analysis in spin-gapped quantum magnets with anisotropic interactions.

Findings

Magnetization fluctuations peak at the crossover temperature.

Heat capacity is smeared out due to Dzyaloshinsky-Moriya interaction.

Sharp fluctuation maxima serve as indicators of the critical temperature.

Abstract

We address the problem of identifying the critical temperature in a crossover from the Bose-Einstein condensed (BEC) phase to the normal phase. For this purpose we study the temperature dependence of magnetization of spin-gapped quantum magnets described by BEC of triplons. We have calculated the heat capacity $C_H$ at constant field and fluctuations in magnetization in a spin-gapped quantum magnet using the Hartree-Fock-Bogouliubov approximation and found optimized parameters of the Hamiltonian of triplon gas. In the region of phase transition, the heat capacity $C_H$ is smeared out due to the Dzyaloshinsky-Moriya (DM) interaction. The sharp maximum of the fluctuations in the magnetization is identified as the critical temperature of the crossover.