Symmetry Demanded Topological Nodal-line Materials

TL;DR

This paper reviews topological nodal line semimetals, focusing on symmetry protection mechanisms, introduces a new material KCu$_2$EuTe$_4$ with Weyl nodal lines near the Fermi level, and discusses experimental signatures of their exotic properties.

Contribution

It provides a comprehensive review of symmetry mechanisms in topological nodal line semimetals and introduces a new material with Weyl nodal lines close to the Fermi level.

Findings

Identification of three symmetry protection mechanisms.

Introduction of KCu$_2$EuTe$_4$ as a new Weyl nodal line material.

Discussion of experimental signatures for nodal line physics.

Abstract

The realization of Dirac and Weyl physics in solids has made topological materials one of the main focuses of condensed matter physics. Recently, the topic of topological nodal line semimetals, materials in which Dirac or Weyl-like crossings along special lines in momentum space create either a closed ring or line of degeneracies, rather than discrete points, has become a hot topic in topological quantum matter. Here we review the experimentally confirmed and theoretically predicted topological nodal line semimetals, focusing in particular on the symmetry protection mechanisms of the nodal lines in various materials. Three different mechanisms: a combination of inversion and time-reversal symmetry, mirror reflection symmetry, and non-symmorphic symmetry, and their robustness under the effect of spin orbit coupling are discussed. We also present a new Weyl nodal line material, the Te-square net compound KCu$_2$EuTe$_4$, which has several Weyl nodal lines including one extremely close to the Fermi level ($<$30 meV below E$_F$). Finally, we discuss potential experimental signatures for observing exotic properties of nodal line physics.