Stabilization of a nonlinear bullet coexisting with a Bose-Einstein condensate in a rapidly cooled magnonic system driven by a spin-orbit torque

TL;DR

This paper demonstrates that longer electric current pulses can create a stabilized nonlinear magnonic bullet coexisting with a magnon Bose-Einstein Condensate in a rapidly cooled magnonic system driven by spin-orbit torque.

Contribution

It introduces a method to stabilize nonlinear magnonic bullets alongside magnon BECs using longer current pulses and rapid cooling in a spin-orbit torque driven system.

Findings

Longer current pulses trigger nonlinear magnonic bullets.

Magnon BECs form at the bottom of the linear spectrum.

Nonlinear bullets persist for 30 ns after pulse termination.

Abstract

We have recently shown that injection of magnons into a magnetic dielectric via the spin-orbit torque (SOT) effect in the adjacent layer of a heavy metal subjected to the action of short (0.1 $\mu$s) current pulses allows for control of a magnon Bose-Einstein Condensate (BEC). Here, the BEC was formed in the process of rapid cooling (RC), when the electric current heating the sample is abruptly terminated. In the present study, we show that the application of a longer (1.0 $\mu$s) electric current pulse triggers the formation of a nonlinear localized magnonic bullet below the linear magnon spectrum. After pulse termination, the magnon BEC, as before, is formed at the bottom of the linear spectrum, but the nonlinear bullet continues to exist, stabilized for additional 30 ns by the same process of RC-induced magnon condensation. Our results suggest that a stimulated condensation of excess magnons to all highly populated magnonic states occurs.