Emerging nonequilibrium bound state in spin-current-local-spin scattering

TL;DR

This paper investigates how a spin current interacts with a ferromagnetic spin chain, revealing a novel non-equilibrium bound state that influences spin-flip dynamics and could impact quantum magnetic control.

Contribution

It introduces and analyzes a new non-equilibrium bound state arising from inelastic scattering in spin-current and local-spin interactions.

Findings

Discovery of a non-equilibrium bound state (NEBS) in spin-current scattering.

NEBS causes itinerant spins to linger before diffusing away.

The phenomenon affects spin-flip dynamics and filtering in quantum spin systems.

Abstract

Magnetization reversal is a well-studied problem with obvious applicability in computer hard-drives. One can accomplish a magnetization reversal in at least one of two ways: application of a magnetic field, or through a spin current. The latter is more amenable to a fully quantum mechanical analysis. We formulate and solve the problem whereby a spin current interacts with a ferromagnetic Heisenberg spin chain, to eventually reverse the magnetization of the chain. Spin-flips are accomplished through both elastic and inelastic scattering. A consequence of the inelastic scattering channel, when it is no longer energetically possible, is the occurrence of a new entity: a non-equilibrium bound state (NEBS), which is an emergent property of the coupled local plus itinerant spin system. For certain definite parameter values the itinerant spin lingers near the local spins for some time, before eventually leaking out as an outwardly diffusing state. This phenomenon results in novel spin-flip dynamics and filtering properties for this type of system.