Intrinsic Negative Magnetoresistance in Layered AFM Semimetals: the Case of EuSn$_2$As$_2$

TL;DR

This study investigates the intrinsic negative magnetoresistance in layered antiferromagnetic semimetals, specifically EuSn$_2$As$_2$, combining experimental measurements and theoretical modeling to explain its origin.

Contribution

The paper introduces a comprehensive experimental and theoretical analysis of negative magnetoresistance in EuSn$_2$As$_2$, proposing a novel mechanism involving exchange splitting and spin-dependent electron confinement.

Findings

Negative magnetoresistance is sample-independent and temperature-dependent.

Theoretical model aligns with ARPES and DFT data.

Magnetoresistance linked to exchange splitting and spin confinement.

Abstract

Here, by applying a comprehensive approach including magnetic, transport measurements, ARPES band structure measurements, DFT calculations, and analytical theory consideration, we unveil the puzzling origin of the negative isotropic magnetoresistance in the highly anisotropic semimetals, particularly, Eu$_2$Sn$_2$As$_2$ with AFM ordering of Eu atoms. The isotropic magnetoresistance developing along with the magnetization changes up to the complete spin polarization field was reported previously in several experimental studies, though its theoretical explanation was missing up to date. Recently, we proposed a novel theoretical mechanism to describe the observed magnetoresistance in layered AFM compounds by exchange splitting of the electron energy levels and by confining the electron wave functions with different spin projection in the vicinity of the respective magnetic layer. In this paper, we present more detailed experimental studies of the negative magnetoresistance with several samples of EuSn$_2$As$_2$ in order to identify its sample-independent features including temperature dependence. We also substantiate the proposed theory by comparing it with magnetotransport data, with ARPES measurements of the energy band structure, and DFT energy spectrum calculations.