Topological metal state in helimagnets

TL;DR

This paper develops a theory for topological band structures in metallic helimagnets, revealing unique electron spin textures and transport phenomena linked to their nontrivial topology.

Contribution

It proves two theorems on electron dispersion in helimagnets and introduces a 2D model explaining topological metal states in specific layered materials.

Findings

Reveals Kramers-like degeneracy in helimagnets

Shows nontrivial topological band structure leads to unusual spin textures

Demonstrates abnormal conductivity and nonreciprocity in modeled systems

Abstract

A theory for nontrivial topology of band structure in metallic helimagnets is developed. Two theorems on electron dispersion in helimagnets are proved. They reveal a Kramers-like degeneracy in helical magnetic field. The generalized Bloch theorem together with periodic boundary conditions lead to a nontrivial topological band structure. As a result, an unusual spin structure of electron bands appears. A 2D model of nearly free electrons is proposed to describe conductive hexagonal palladium layers under an effective field of magnetically ordered CrO$_2$ spacers in PdCrO$_2$. The spin texture of the Fermi surface induces abnormal conductivity and nonreciprocity of electronic transport. It is shown that the topological metal state is closely related to unconventional antiferromagnets.