Effects of dilution in a 2D topological magnon insulator

Abstract

We study the effect of diluting a two-dimensional ferromagnetic insulator hosting a topological phase in the clean limit. By considering the ferromagnetic Heisenberg model in the honeycomb lattice with second nearest-neighbor Dzyanshikii-Moriya interaction, and working in the linear spin-wave approximation, we establish the topological phase diagram as a function of the fraction $p$ of diluted magnetic atoms. The topological phase with Chern number $C=1$ is robust up to a moderate dilution $p_{1}^{*}$, while above a higher dilution $p_{2}^{*}>p_{1}^{*}$ the system becomes trivial. Interestingly, both $p_{1}^{*}$ and $p_{2}^{*}$ are below the classical percolation threshold $p_{c}$ for the honeycomb lattice, which gives physical significance to the obtained phases. In the topological phase for $p p_{2}^{*}$, when all states become localized, the system shows $C=0$ as expected for a trivial phase. Replacing magnetic with non-magnetic atoms in a systems hosting a magnon Chern insulator in the clean limit puts all the three phases within experimental reach.