Discovery of a Weyl Semimetal in non-Centrosymmetric Compound TaAs

TL;DR

This paper reports the discovery of the first three-dimensional Weyl semimetal in the non-centrosymmetric compound TaAs, confirmed through experimental measurements aligning with theoretical predictions, revealing unique topological electronic structures.

Contribution

The study provides the first experimental observation of a 3D Weyl semimetal in TaAs, demonstrating its topological features and confirming theoretical models.

Findings

Observation of Fermi-arc surface states

Linear bulk band dispersion across Weyl points

Agreement with theoretical calculations

Abstract

Three-dimensional (3D) topological Weyl semimetals (TWSs) represent a novel state of quantum matter with unusual electronic structures that resemble both a "3D graphene" and a topological insulator by possessing pairs of Weyl points (through which the electronic bands disperse linearly along all three momentum directions) connected by topological surface states, forming the unique "Fermi-arc" type Fermi-surface (FS). Each Weyl point is chiral and contains half of the degrees of freedom of a Dirac point, and can be viewed as a magnetic monopole in the momentum space. Here, by performing angle-resolved photoemission spectroscopy on non-centrosymmetric compound TaAs, we observed its complete band structures including the unique "Fermi-arc" FS and linear bulk band dispersion across the Weyl points, in excellent agreement with the theoretical calculations. This discovery not only confirms TaAs as the first 3D TWS, but also provides an ideal platform for realizing exotic physical phenomena (e.g. negative magnetoresistance, chiral magnetic effects and quantum anomalous Hall effect) which may also lead to novel future applications.