Kitaev-Heisenberg model on the star lattice: From chiral Majorana fermions to chiral triplons

TL;DR

This paper explores the rich phase diagram of the Kitaev-Heisenberg model on the star lattice, revealing valence bond solid phases, chiral quantum spin liquids, and chiral triplon excitations with high Chern numbers influenced by lattice geometry and exchange interactions.

Contribution

It uncovers new valence bond solid and chiral spin liquid phases in the Kitaev-Heisenberg model on the star lattice, highlighting the emergence of chiral triplons with high Chern numbers.

Findings

Identification of VBS and chiral spin liquid phases

Tuning between phases via exchange ratio

Chiral triplons with high Chern numbers

Abstract

The interplay of frustrated interactions and lattice geometry can lead to a variety of exotic quantum phases. Here we unearth a particularly rich phase diagram of the Kitaev-Heisenberg model on the star lattice, a triangle decorated honeycomb lattice breaking sublattice symmetry. In the antiferromagnetic regime, the interplay of Heisenberg coupling and geometric frustration leads to the formation of valence bond solid (VBS) phases -- a singlet VBS and a bond selective triplet VBS stabilized by the Kitaev exchange. We show that the ratio of the Kitaev versus Heisenberg exchange tunes between these VBS phases and chiral quantum spin liquid regimes. Remarkably, the VBS phases host a whole variety of chiral triplon excitations with high Chern numbers in the presence of a weak magnetic field. We discuss our results in light of a recently synthesized star lattice material and other decorated lattice systems.