Stability of Bose Einstein condensates of hot magnons in YIG

TL;DR

This paper studies the stability of room temperature magnon Bose-Einstein condensates in YIG, revealing their metastability under current conditions and proposing a new geometry for stable, high-density condensates.

Contribution

It demonstrates the dependence of magnon-magnon interactions on external field orientation and predicts a stable, high-density BEC in a perpendicular magnetic field geometry.

Findings

Magnon-magnon interactions depend strongly on field orientation.

Current BECs are metastable due to finite size effects and low density.

Perpendicular magnetic fields can lead to stable, high-density magnon BECs.

Abstract

We investigate the stability of the recently discovered room temperature Bose-Einstein condensate (BEC) of magnons in Ytrrium Iron Garnet (YIG) films. We show that magnon-magnon interactions depend strongly on the external field orientation, and that the BEC in current experiments is actually metastable - it only survives because of finite size effects, and because the BEC density is very low. On the other hand a strong field applied perpendicular to the sample plane leads to a repulsive magnon-magnon interaction; we predict that a high-density magnon BEC can then be formed in this perpendicular field geometry.