Antichiral surface states and Su-Schrieffer-Heeger physics in rutile altermagnets

TL;DR

This paper uncovers the existence of anti-chiral surface states in rutile altermagnets, linked to Weyl nodal lines, and demonstrates their tunability via surface termination, expanding the understanding of topological surface phenomena.

Contribution

It introduces the concept of anti-chiral surface states in altermagnets and connects them to a modified SSH model, providing a new perspective on surface state topology in quantum materials.

Findings

Discovery of anti-chiral surface states in rutile altermagnets.

Surface states can switch from anti-chiral to chiral by changing surface termination.

Surface states originate from Weyl nodal lines and are explained via a modified SSH model.

Abstract

We study surface states and domain wall bound states in altermagnets using a rutile-lattice tight-binding model of electrons coupled to a N\'eel order. We discover that two symmetry-protected Weyl nodal lines in the bulk band structure can give rise to unconventional anti-chiral surface states -- surface states from opposite surfaces propagate in a \emph{parallel} manner, as opposed to the anti-parallel manner for the more conventional chiral surface states. We also find that the anti-chiral surface states can be turned into chiral surface states upon changing the surface termination. The origin of the surface states, the dependence on the surface termination, and key features of domain wall bound states are explained using a map from the altermagnet to a family of a modified Su-Schrieffer-Heeger(SSH) chain and the associated bulk-boundary correspondence. Our work reveals rutile altermagnets as a promising candidate among very few quantum materials that can support anti-chiral surface states.