Kekule spin-orbit dimer phase and triplon dynamics

TL;DR

This paper introduces a spin-orbital model for d^1 ions on a honeycomb lattice, revealing a Kekule spin-orbit dimer phase with topologically non-trivial triplon bands, and proposes thermal Hall measurements for experimental verification.

Contribution

It demonstrates how charge transfer interactions stabilize a Kekule dimerized phase with topological triplon bands in a spin-orbital model.

Findings

Degenerate dimerized ground states are stabilized into a Kekule phase by charge transfer.

Triplon band spectrum resembles kagome lattice electronic bands and exhibits topological features.

Thermal Hall effect can be used to detect the topological triplon bands.

Abstract

We derive and study a spin-orbital model for ions with $d^1$ electronic configuration on a honeycomb lattice. In this system, the directional character of $t_{2g}$ orbital leads to extensively degenerate dimerized ground states. We find that additional interactions from charge transfer processes completely lift the degeneracy and stabilize the Kekule spin-orbit dimerized phase where dimers form a kagome superlattice. For such phase, the triplon band spectrum resembles the electronic band structure of the kagome lattice and becomes topologically non-trivial in the presence of inter-dimer Dzyaloshinskii-Moriya interactions. As an experimental verification of the Kekule dimerized phase, we propose the thermal Hall experiment, which can directly uncover the topological profile of the corresponding triplon band spectrum.