Non-trivial topology of the quasi-one-dimensional triplons in the quantum antiferromagnet ${\text{BiCu}}_{2}{\text{PO}}_{6}$

TL;DR

This paper demonstrates that the quantum antiferromagnet ${\text{BiCu}}_{2}{\text{PO}}_{6}$ exhibits topologically non-trivial triplon excitations characterized by a finite Zak phase, revealing novel topological properties in magnetic systems.

Contribution

It is the first gapful quantum antiferromagnet with a finite Zak phase and the second with topological non-trivial triplon excitations, highlighting unique topological phenomena.

Findings

${\text{BiCu}}_{2}{\text{PO}}_{6}$ has a finite Zak phase indicating non-trivial topology.

No localized edge modes are observed despite bulk-boundary correspondence.

The absence of edge modes is explained by differences between direct and indirect gaps.

Abstract

Topological properties of physical systems are attracting tremendous interest. Recently, magnetic solid state compounds with and without magnetic order have become a focus. We show that ${\text{BiCu}}_{2}{\text{PO}}_{6}$ is the first gapful quantum antiferromagnet with a finite Zak phase, which characterises one-dimensional systems, and only the second with topological non-trivial triplon excitations. Surprisingly, in spite of the bulk-boundary correspondence no localised edge mode occurs. This unexpected behaviour is explained by the distinction between direct and indirect gaps among the triplon bands.