Exchange Splitting Mechanism of Negative Magnetoresistance in Layered Antiferromagnetic Semimetals

TL;DR

This paper proposes a new intrinsic theoretical mechanism explaining negative magnetoresistance in layered antiferromagnetic semimetals, aligning well with experimental observations without relying on topological effects or defects.

Contribution

It introduces a novel theoretical explanation for negative magnetoresistance in layered AFM semimetals, independent of topological or defect-related factors.

Findings

The mechanism explains quadratic decrease in resistance with magnetic field.

Theoretical results qualitatively match experimental data across various materials.

The proposed model applies broadly to layered AFM-ordered semimetals.

Abstract

Layered topologically non-trivial and trivial semimetals with AFM-type ordering of magnetic sublattice are known to exhibit a negative magnetoresistance that is well correlated with AFM magnetization changes in a magnetic field. This effect is reported in several experimental studies with EuFe$_2$As$_2$, EuSn$_2$As$_2$, EuSn$_2$P$_2$, etc., where the resistance decreases quadratically with field by about $\delta\rho/\rho \sim 4-6\%$ up to the spin-polarization field. Despite the fact that this effect is well documented experimentally, its theoretical explanation is missing up to date. In this paper we propose a novel theoretical mechanism describing the observed magnetoresistance that does not imply either topological origin of the materials, surface roughness, their potential defect structure, or electron-magnon scattering. We believe, the proposed intrinsic mechanism of magnetoresistance is applicable to a wide class of the layered AFM- ordered semimetals. The theoretically calculated magnetoresistance is qualitatively consistent with experimental data for crystals of various composition.