Two-Fluid Theory for Spin Superfluidity in Magnetic Insulators

TL;DR

This paper develops a two-fluid hydrodynamic model for spin superfluidity in magnetic insulators, linking thermal and condensed magnons, and proposes experimental detection via spin Seebeck effect.

Contribution

It introduces a novel two-fluid theoretical framework combining Gross-Pitaevski and magnetoelectric theories for spin superfluidity in magnetic insulators.

Findings

Derived boundary conditions for hybrid heterostructures.

Proposed experimental method to detect spin superfluidity.

Established conditions for phase transition between normal and condensate states.

Abstract

We investigate coupled spin and heat transport in easy-plane magnetic insulators. These materials display a continuous phase transition between normal and condensate states that is controlled by an external magnetic field. Using hydrodynamic equations supplemented by Gross-Pitaevski phenomenology and magnetoelectric circuit theory, we derive a two-fluid model to describe the dynamics of thermal and condensed magnons, and the appropriate boundary conditions in a hybrid normal-metal|magnetic-insulator|normal-metal heterostructure. We discuss how the emergent spin superfluidity can be experimentally probed via a spin Seebeck effect measurement.