Time-Reversal Symmetry Breaking Type-II Weyl State in YbMnBi2

TL;DR

This paper reports the experimental discovery of a time-reversal symmetry breaking Type-II Weyl state in YbMnBi2, confirmed through magnetization and angle-resolved photoemission measurements, linking high-energy and condensed-matter physics.

Contribution

It provides the first experimental evidence of a magnetic Weyl state in a material with high Fermi velocities, demonstrating a practical approach to designing exotic quantum materials.

Findings

Identification of Weyl points above and below the Fermi level

Observation of surface state arcs connecting Weyl points

Modeling of magnetic structure as canted antiferromagnetism

Abstract

Detection of Dirac, Majorana and Weyl fermions in real materials may significantly strengthen the bridge between high-energy and condensed-matter physics. While the presence of Dirac fermions is well established in graphene and topological insulators, Majorana particles have been reported recently and evidence for Weyl fermions in non-centrosymmetric crystals has been found only a couple of months ago, the 'magnetic' Weyl fermions are still elusive despite numerous theoretical predictions and intense experimental search. In order to detect a time-reversal symmetry breaking Weyl state we designed two materials with Fermi velocities superior to that of graphene and present here the experimental evidence of the realization of such a state in one of them, YbMnBi2. We model the time reversal symmetry breaking observed by magnetization measurements by a canted antiferromagnetic state and find a number of Weyl points both above and below the Fermi level. Using angle-resolved photoemission, we directly observe these latter Weyl points and a hallmark of the exotic state - the arc of the surface states which connects these points. Our results not only provide a fundamental link between the two areas of physics, but also demonstrate the practical way to design novel materials with exotic properties.