Topological Materials: Weyl Semimetals

TLDR

Topological insulators and semimetals are quantum materials whose surface states arise from bulk band topology, with Dirac/Weyl semimetals exhibiting linear dispersion at nodes analogous to graphene and tunable properties across large material families. The article reviews and compares topological states of matter, focusing on Weyl semimetals, to provide a concise introduction to the rapidly expanding field. The review examines the TaAs family and Heusler compounds to illustrate Weyl point signatures such as Fermi arcs and chiral magneto‑transport, and discusses searches for type‑II Weyl semimetals in WTe₂, MoTe₂, and related materials.

Abstract

Topological insulators and topological semimetals are both new classes of quantum materials, which are characterized by surface states induced by the topology of the bulk band structure. Topological Dirac or Weyl semimetals show linear dispersion round nodes, termed the Dirac or Weyl points, as the three-dimensional analogue of graphene. We review the basic concepts and compare these topological states of matter from the materials perspective with a special focus on Weyl semimetals. The TaAs family is the ideal materials class to introduce the signatures of Weyl points in a pedagogical way, from Fermi arcs to the chiral magneto-transport properties, followed by the hunting for the type-II Weyl semimetals in WTe2, MoTe2 and related compounds. Many materials are members of big families and topological properties can be tuned. As one example, we introduce the multifuntional topological materials, Heusler compounds, in which both topological insulators and magnetic Weyl semimetals can be found. Instead of a comprehensive review, this article is expected to serve as a helpful introduction and summary by taking a snapshot of the quickly expanding field.