Electronic Pumping of Quasiequilibrium Bose-Einstein Condensed Magnons

TL;DR

This paper presents a theoretical study of spin transfer in a system of Bose-Einstein condensed magnons, revealing a temperature-independent condensate spin current and the potential for dynamical phase transitions.

Contribution

It introduces a novel theoretical framework for understanding spin transfer involving magnon BEC and predicts a temperature-independent spin current at the interface.

Findings

Bose-Einstein condensation leads to a temperature-independent spin current.

Spin can flow in either direction depending on thermodynamic bias.

Potential for observing a magnon BEC steady state via spin Seebeck effect.

Abstract

We theoretically investigate spin transfer between a system of quasiequilibrated Bose-Einstein condensed magnons in an insulator in direct contact with a conductor. While charge transfer is prohibited across the interface, spin transport arises from the exchange coupling between insulator and conductor spins. In normal insulator phase, spin transport is governed solely by the presence of thermal and spin-diffusive gradients; the presence of Bose-Einstein condensation (BEC), meanwhile, gives rise to a temperature-independent condensate spin current. Depending on the thermodynamic bias of the system, spin may flow in either direction across the interface, engendering the possibility of a dynamical phase transition of magnons. We discuss experimental feasibility of observing a BEC steady state (fomented by a spin Seebeck effect), which is contrasted to the more familiar spin-transfer induced classical instabilities.