Stability of chiral magnon condensates in collinear antiferromagnetic insulators

TL;DR

This paper investigates the stability of chiral magnon Bose-Einstein condensates in antiferromagnetic insulators, revealing the importance of two-component condensation and interactions for metastability, and identifying conditions for stable condensates.

Contribution

It provides a detailed analysis of conditions for stable magnon condensation in antiferromagnets, highlighting the role of two-component systems and interactions, which was not previously explored.

Findings

Two-component magnon condensation is crucial for metastability.

Symmetric magnon distribution supports stable condensation in uniaxial systems.

Biaxial systems without Dzyaloshinskii-Moriya interaction cannot stabilize magnon condensates.

Abstract

Quasiequilibrium magnon Bose-Einstein condensates in ferromagnetic insulators have been a field of great interest, while condensation in antiferromagnetic systems has not yet been explored in detail. We analyze the stability of condensed chiral magnons in two antiferromagnetic insulators: a uniaxial easy-axis system and a biaxial system. We show that two-component magnon condensation and inter-magnon interactions are essential to create metastable magnon condensation. The uniaxial system with a Rashba-type Dzyaloshinskii-Moriya interaction supports two degenerate condensate populations at finite wave vectors. We find that the condensation state in this model is (meta)stable only when the distribution of condensed magnons between the two populations is symmetric. In addition, we demonstrate the emergence of a zero-sound-like Goldstone mode in antiferromagnetic systems that support two-component magnon condensation. On the other hand, in the biaxial system without Dzyaloshinskii-Moriya interaction, we predict that the magnon condensate cannot stabilize due to the breaking of the magnon degeneracy. Our results suggest that this instability is a general characteristic of single-component quasiequilibrium quasiparticle condensates.