From Kinetic Instability to Bose-Einstein Condensation and Magnon Supercurrents

TL;DR

This study demonstrates room-temperature Bose-Einstein condensation of magnons and magnon supercurrents in yttrium iron garnet, revealing that kinetic instability enhances condensate density and supercurrent strength compared to turbulence cascade.

Contribution

It shows that kinetic instability significantly boosts magnon condensate density and supercurrent, providing new insights into magnon condensation mechanisms at room temperature.

Findings

Kinetic instability results in denser magnon condensates.

Stronger magnon supercurrents are observed with kinetic instability.

The process is studied across various magnetic fields.

Abstract

Evolution of an overpopulated gas of magnons to a Bose-Einstein condensate and excitation of a magnon supercurrent, propelled by a phase gradient in the condensate wave function, can be observed at room-temperature by means of the Brillouin light scattering spectroscopy in an yttrium iron garnet material. We study these phenomena in a wide range of external magnetic fields in order to understand their properties when externally pumped magnons are transferred towards the condensed state via two distinct channels: A multistage Kolmogorov-Zakharov cascade of the weak-wave turbulence or a one-step kinetic-instability process. Our main result is that opening the kinetic instability channel leads to the formation of a much denser magnon condensate and to a stronger magnon supercurrent compared to the cascade mechanism alone.