Non-trivial topology of the quasi-one-dimensional triplons in the quantum antiferromagnet ${\text{BiCu}}_2{\text{PO}}_6$

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.

12 pages main text (3 figures), 14 pages supplemental materials (3 figures)