Nontrivial Berry phase in magnetic BaMnSb2 semimetal

TL;DR

This paper reports the experimental discovery of a magnetic Weyl semimetal, BaMnSb2, which exhibits a nontrivial Berry phase and breaks time-reversal symmetry due to its magnetic ordering, providing a platform for studying magnetic Weyl fermions.

Contribution

It demonstrates that canted antiferromagnetic BaMnSb2 is a 3D Weyl semimetal with a 2D electronic structure and nontrivial Berry phase, highlighting magnetic order as a symmetry-breaking mechanism.

Findings

BaMnSb2 exhibits nearly zero effective mass and high mobility.

The material shows a nontrivial Berry phase in quantum oscillations.

Magnetic ordering breaks time-reversal symmetry, enabling Weyl fermions.

Abstract

The subject of topological materials has attracted immense attention in condensed-matter physics, because they host new quantum states of matter containing Dirac, Majorana, or Weyl fermions. Although Majorana fermions can only exist on the surface of topological superconductors, Dirac and Weyl fermions can be realized in both 2D and 3D materials. The latter are semimetals with Dirac/Weyl cones either not tilted (type I) or tilted (type II). Although both Dirac and Weyl fermions have massless nature with the nontrivial Berry phase, the formation of Weyl fermions in 3D semimetals require either time-reversal or inversion symmetry breaking to lift degeneracy at Dirac points. Here, we demonstrate experimentally that canted antiferromagnetic BaMnSb2 is a 3D Weyl semimetal with a 2D electronic structure. The Shubnikov-de Hass oscillations of the magnetoresistance give nearly zero effective mass with high mobility and the nontrivial Berry phase. The ordered magnetic arrangement (ferromagnetic ordering in the ab plane and antiferromagnetic ordering along the c axis below 286 K) breaks the time-reversal symmetry, thus offering us an ideal platform to study magnetic Weyl fermions in a centrosymmetric material.