Multipolar edge states in the breathing kagome model

TL;DR

This paper investigates topologically nontrivial multiplet excitations in a breathing kagome quantum magnet, revealing tunable band touchings, large Chern numbers, and novel quadrupolar edge states, advancing understanding of magnetic topological phenomena.

Contribution

It introduces the study of multipolar topological excitations in the breathing kagome model, including the discovery of a spin-3/2 Dirac cone and quadrupolar edge modes.

Findings

Identification of spin-1/2 doublet and spin-3/2 quartet excitations.

Observation of a topological phase transition with a spin-3/2 Dirac cone.

Detection of large Chern numbers and quadrupolar edge states.

Abstract

Excitations of ordered insulating magnets gain renewed interest due to their potential topological properties and the natural realization of magnetic analogues of the celebrated topological models. In this paper we go beyond these parallels and explore what else is there in the unconventional excitations of quantum magnets. We study the topologically nontrivial multiplet excitations of the antiferromagnetic spin-1/2 kagome system with strong breathing anisotropy and Dzyaloshinskii-Moriya interaction. We show that in the chiral magnetic ground state the excitations can be characterized by a spin-1/2 doublet and a spin-3/2 quartet. With the use of magnetic field we can tune the quartet through a band touching topological phase transition, when a novel spin-3/2 Dirac cone is formed by the touching of four bands. In the topologically nontrivial regime the spin-3/2 bands have large Chern numbers -3, -1, 1, 3. In an open system the emerging chiral edge states naturally inherit the multipolar characters and we find novel quadrupolar edge modes.