Slow inter-minima relaxation and its consequence for BEC of magnons

TL;DR

This paper investigates how slow relaxation between energy minima affects the properties of magnon Bose-Einstein condensates, challenging previous theories that assumed fast relaxation processes.

Contribution

It introduces an analytic theory for slow inter-minima relaxation and examines its impact on magnon BEC properties, addressing discrepancies with experimental observations.

Findings

Slow inter-minima relaxation alters expected magnon BEC behavior

Existing theories assume fast relaxation, which is contradicted by experimental data

Analytic classification of relaxation processes provides new insights

Abstract

Two recent articles of the Munster University experimental team led by S.O. Demokritov displayed several important facts related to the Bose-Einstein condensation of magnons (BECM) under permanent pumping first discovered in 2006. They contradicted existing theories of this phenomenon, which predict the attractive interaction between magnons and strong spontaneous violation of the reflection symmetry. In this article, we show that these theories implicitly assumed all relaxation processes to be fast compared with the lifetime of the magnons, whereas one of them -- relaxation between two minima of energy -- is slow. We classify processes responsible for the inter-minima relaxation and present their analytic theory. We analyze how the slow inter-minima relaxation modifies the anticipated properties of a ferromagnet with the magnon condensate.