Spin excitations in systems with hopping electron transport and strong position disorder in a large magnetic field

TL;DR

This paper investigates how spin excitations behave in disordered systems with hopping electrons under strong magnetic fields, revealing conditions for delocalization and implications for spin transport in devices.

Contribution

It demonstrates that in 3D disordered systems, spin excitations can be delocalized, enabling coherent spin transport even with strong disorder, and explores localization effects due to magnetic field inhomogeneities.

Findings

Delocalized spin excitations exist in 3D systems with strong disorder.

Non-homogeneous magnetic fields cause Anderson localization of spin excitations.

Exchange anisotropy leads to Lifshitz localization of excitations.

Abstract

We discuss the spin excitations in systems with hopping electron conduction and strong position disorder. We focus on the problem in a strong magnetic field when the spin Hamiltonian can be reduced to the effective single-particle Hamiltonian and treated with conventional numerical technics. It is shown that in a 3D system with Heisenberg exchange interaction the spin excitations have a delocalized part of the spectrum even in the limit of strong disorder, thus leading to the possibility of the coherent spin transport. The spin transport provided by the delocalized excitations can be described by a diffusion coefficient. Non-homogenous magnetic fields lead to the Anderson localization of spin excitations while anisotropy of the exchange interaction results in the Lifshitz localization of excitations. We discuss the possible effect of the additional exchange-driven spin diffusion on the organic spin-valve devices.