Monopole Charge Density Wave States in Weyl Semimetals

TL;DR

This paper introduces a novel class of topological charge density wave states in Weyl semimetals, characterized by monopole harmonic symmetries and non-trivial Berry phases, leading to unique nodal structures and surface states.

Contribution

It reveals how Fermi surface nesting and band topology induce monopole charge density wave states with topologically protected nodal Weyl points.

Findings

Density-wave states exhibit monopole harmonic symmetries.

Nodal gap functions host zero-energy Weyl nodes.

Topologically protected Fermi arc surface states emerge.

Abstract

We study a new class of topological charge density wave states exhibiting monopole harmonic symmetries. The density-wave ordering is equivalent to pairing in the particle-hole channel due to Fermi surface nesting under interactions. When electron and hole Fermi surfaces carry different Chern numbers, the particle-hole pairing exhibits a non-trivial Berry phase inherited from band structure topology independent of concrete density-wave ordering mechanism. The associated density-wave gap functions become nodal, and the net nodal vorticity is determined by the monopole charge of the pairing Berry phase. The gap function nodes become zero-energy Weyl nodes of the bulk spectra of quasi-particle excitations. These states can occur in doped Weyl semimetals with nested electron and hole Fermi surfaces enclosing Weyl nodes of the same chirality in the weak coupling regime. Topologically non-trivial low-energy Fermi arc surface states appear in the density-wave ordering state as a consequence of the emergent zero-energy Weyl nodes.