Ultraquantum magnetoresistance in Kramers Weyl semimetal candidate $\beta$-Ag2Se

TL;DR

This study reveals ultraquantum magnetoresistance phenomena in the Kramers Weyl semimetal candidate $eta$-Ag2Se, demonstrating quantum limit behavior and Berry-phase effects through combined experimental measurements and theoretical analysis.

Contribution

It provides the first experimental observation of ultraquantum magnetoresistance in a Kramers Weyl semimetal, supported by comprehensive theoretical band structure calculations.

Findings

Giant Shubnikov-de Haas oscillations from a small electron pocket

Negative longitudinal magnetoresistance beyond the quantum limit

Berry-phase structure associated with Weyl nodes

Abstract

The topological semimetal $\beta$-Ag2Se features a Kramers Weyl node at the origin in momentum space and a quadruplet of spinless Weyl nodes, which are annihilated by spin-orbit coupling. We show that single crystalline $\beta$-Ag2Se manifests giant Shubnikov-de Haas oscillations in the longitudinal magnetoresistance which stem from a small electron pocket that can be driven beyond the quantum limit by a field less than 9 T. This small electron pocket is a remainder of the spin-orbit annihilatedWeyl nodes and thus encloses a Berry-phase structure. Moreover, we observed a negative longitudinal magnetoresistance when the magnetic field is beyond the quantum limit. Our experimental findings are complemented by thorough theoretical band structure analyses of this Kramers Weyl semimetal candidate, including first-principle calculations and an effective k*p model.