High-field instability of field-induced triplon Bose-Einstein condensate

TL;DR

This paper investigates the behavior of a triplon Bose-Einstein condensate under high magnetic fields, revealing the effects of interactions and dispersion on its stability and phase transitions.

Contribution

It introduces a detailed theoretical analysis of the high-field instability of the triplon BEC, accounting for anomalous density and nonparabolic dispersion effects.

Findings

Magnetization remains continuous across the transition, matching experimental observations.

The condensate becomes unstable at high fields due to triplon-triplon repulsion.

Two critical magnetic fields define the formation and destruction of the condensate.

Abstract

We study properties of magnetic field-induced Bose-Einstein condensate of triplons as a function of temperature and the field within the Hartree-Fock-Bogoliubov approach including the anomalous density. We show that the magnetization is continuous across the transition, in agreement with the experiment. In sufficiently strong fields the condensate becomes unstable due to triplon-triplon repulsion. As a result, the system is characterized by two critical magnetic fields: one producing the condensate and the other destroying it. We show that nonparabolic triplon dispersion arising due to the gapped bare spectrum and the crystal structure has a strong influence on the phase diagram.