Direct observation of magnon BEC in an out-of-plane magnetized yttrium iron garnet film

TL;DR

This paper reports the first direct observation of magnon Bose-Einstein condensation in an out-of-plane magnetized yttrium iron garnet film, demonstrating a transition to a coherent magnon state via microwave pumping.

Contribution

It provides experimental evidence of magnon BEC in yttrium iron garnet, using optical methods to observe the spatial distribution and phase of the condensed magnons, which is a novel achievement.

Findings

Transition from spin wave to magnon BEC observed

Coherent stationary magnon state demonstrated

Optical methods used to map magnon density and phase

Abstract

Bose-Einstain condensation occurs at an appropriate density of bosonic particles, depending on their mass and temperature. We were able to experimentally observe the transition from the spin wave regime to the magnon Bose-Einstein condensed state (mBEC) with increasing magnon density by a microwave pumping. We used optical methods to register the spatial distribution of the magnon density and phase. For the first time, a coherent state of stationary magnons was demonstrated far from the region of their excitation.