Turning Copper Metal into Weyl Semimetal

TL;DR

This paper introduces a novel mechanism for realizing Weyl semimetals by band inversion involving d states in copper compounds, expanding the search for topological materials beyond traditional s-p inversions.

Contribution

It proposes a new band inversion mechanism involving d states in copper compounds and identifies specific materials as Weyl semimetals or topological insulators.

Findings

CuF is an ideal Weyl semimetal with 24 Weyl nodes.

CuNaO and CuLiO are s-d inversion topological insulators.

The study expands the material search space for topological quantum systems.

Abstract

A search for new topological quantum systems is challenging due to the requirement of non{trivial band connectivity that leads to protected surface states of electrons. A progress in this field was primarily due to a realization of band inversion mechanism between even and odd parity states that was proven to be very useful in both predicting many of such systems and our understanding their topological properties. Despite many proposed materials assume the band inversion between s and p (or p/d, d/f) electrons, here, we explore a different mechanism where the occupied d states subjected to a tetrahedral crystal field produce an active t2g manifold behaving as a state with an effective orbital momentum equal to negative one, and pushing jeff = 1=2 doublet at a higher energy. Via hybridization with nearest neighbor orbitals realizable, e.g., in a zincblende structural environment, this allows a formation of odd parity state whose subsequent band inversion with an unoccupied s band becomes possible, prompting us to look for the compounds with Cu+1 ionic state. Chemical valence arguments coupled to a search in materials database lead us to systematically investigate electronic structures and topological properties of CuY (Y=F, Cl, Br, I) and CuXO (X=Li, Na, K, Rb) families of compounds. Our theoretical results show that CuF displays a behavior characteristic of an ideal Weyl semimetal with 24 Weyl nodes at the bulk Brillouin Zone. We also find that another compounds CuNaO and CuLiO are the s-d inversion type topological insulators. Results for their electronic structures and corresponding surfaces states are presented and discussed in the context of their topological properties.