Theory for the negative longitudinal magnetoresistance in the quantum limit of Kramers Weyl semimetals

TL;DR

This paper develops a theoretical explanation for the observed negative magnetoresistance in Kramers Weyl semimetals, specifically in the quantum limit of $eta$-Ag$_2$Se, without relying on the chiral anomaly.

Contribution

It introduces a theory showing negative magnetoresistance can occur in Kramers Weyl semimetals without chiral anomaly, emphasizing the role of screened Coulomb scattering.

Findings

Negative magnetoresistance can occur without chiral anomaly.

Screened Coulomb scattering is crucial for negative magnetoresistance.

The theory applies to $eta$-Ag$_2$Se and similar materials.

Abstract

Negative magnetoresistance is rare in non-magnetic materials. Recently, a negative magnetoresistance has been observed in the quantum limit of $\beta$-Ag$_2$Se, where only one band of Landau levels is occupied in a strong magnetic field parallel to the applied current. $\beta$-Ag$_2$Se is a material that host a Kramers Weyl cone with band degeneracy near the Fermi energy. Kramers Weyl cones exist at time-reversal invariant momenta in all symmorphic chiral crystals, and at a subset of these momenta, including the $\Gamma$ point, in non-symmorphic chiral crystals. Here, we present a theory for the negative magnetoresistance in the quantum limit of Kramers Weyl semimetals. We show that, although there is a band touching similar to those in Weyl semimetals, negative magnetoresistance can exist without a chiral anomaly. We find that it requires screened Coulomb scattering potentials between electrons and impurities, which is naturally the case in $\beta$-Ag$_2$Se.