Hund nodal line semimetals: The case of twisted magnetic phase in the double-exchange model

TL;DR

This paper introduces Hund nodal line semimetals, a new class of topological metals arising from Hund's coupling in the double exchange model, with symmetry-protected band crossings on the Brillouin zone boundary.

Contribution

It identifies a novel topological phase in the double exchange model with a specific twisted spin configuration, highlighting symmetry protections of band crossings.

Findings

Protected band crossings along high-symmetry lines.

Symmetry breaking effects from perturbations.

Potential for surface states and stability analysis.

Abstract

We propose a class of topological metals, which we dub \emph{Hund nodal line semimetals}, arising from the strong Coulomb interaction encoded in the Hund's coupling between itinerant electrons and localized spins. We here consider a particular twisted spin configuration, which is realized in the double exchange model which describes the manganite oxides. The resulting effective tetragonal lattice of electrons with hoppings tied to the local spin features an antiunitary \emph{non-symmorphic} symmetry that in turn, together with another non-symmorphic but unitary, glide mirror symmetry, protects crossings of a double pair of bands along a high-symmetry line on the Brillouin zone boundary. We also discuss symmetry breaking arising from various perturbations of the twisted phase. Our results may motivate further studies of other realizations of this state of matter, for instance in different spin backgrounds, properties of its drumhead surface states, as well as its stability to disorder and interactions among the itinerant electrons.