Crystalline-electromagnetic responses of higher order topological semimetals

TL;DR

This paper investigates the unique electromagnetic responses of higher order Weyl semimetals with quadrupolar Weyl node arrangements, revealing surface and bulk phenomena linked to their topological properties.

Contribution

It introduces a model with quadrupole of higher order Weyl nodes, demonstrating novel surface responses and a bulk quadrupole moment connecting bulk and surface behaviors.

Findings

Higher order Weyl nodes induce dipoles of Dirac nodes on surfaces.

Surface responses include charge binding to dislocations and momentum-density to magnetic fields.

Bulk quadrupole moment links bulk properties to surface phenomena.

Abstract

Previous work has shown that time-reversal symmetric Weyl semimetals with a quadrupolar arrangement of first-order Weyl nodes exhibit a mixed crystalline-electromagnetic response. For systems with higher order Weyl nodes, which are attached to both surface and hinge Fermi arcs, additional phenomena appear on surfaces of codimension $n>1$, such as electromagnetic responses of the hinges. Here we construct a model possessing a quadrupole of higher order Weyl nodes to study the interplay between higher order topology and mixed crystalline-electromagnetic responses. We show that the higher order nature of the Weyl nodes yields a dipole of Dirac nodes on certain surfaces, leading to a mixed crystalline-electromagnetic \emph{surface} response that binds charge to dislocations and momentum-density to magnetic fields. In addition, we show that the model possesses a bulk quadrupole moment of crystal-momentum that provides a link between the bulk and surface responses of the system.