High bosonic Bott index and transport of multi-band topological magnons

TL;DR

This paper explores the topological properties and transport phenomena of multi-band magnons in a Kagome ferromagnetic model, validating the bosonic Bott index as a robust invariant and analyzing disorder effects on magnon transport.

Contribution

It extends the bosonic Bott index to multi-band magnonic systems and investigates their topological phase transitions and transport properties under disorder and damping.

Findings

Bosonic Bott indices larger than 1 are validated in multi-band magnon systems.

Disorder induces multi-step topological phase transitions.

Magnon transport depends on damping and disorder, influenced by topological phases.

Abstract

Magnons are bosonic quasiparticles in magnetically ordered systems. Bosonic Bott index has been affirmed as a real-space topological invariant for a two-band ferromagnetic model. In this work,we theoretically investigate the topology and transport of magnons in a multi-band bosonic Kagome ferromagnetic model. We demonstrate the validity of the bosonic Bott indices of values larger than 1 in multi-band magnonic systems by showing the agreement with Chern numbers in the clean limit and the bulk-boundary correspondence during the topological phase transition. For the high Bott index phase, the disorder-induced topological phase transition occurs in a multi-step manner. Using a generalized Landauer-Buttiker formalism, we reveal how the magnon transport depends on Gilbert damping and disorder under coherent excitation or temperature difference. The results further justify the bosonic Bott index as a robust real-space topological invariant for multi-band magnonic systems and provide insights into the transport of topological magnons.