Tunable magnon topology in monolayer <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>CrI</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math> under external stimuli

Two-dimensional (2D) honeycomb ferromagnets, such as monolayer chromium-trihalides, are predicted to behave topological magnon insulators - characterized by an insulating bulk and topologically protected edge states, giving rise a thermal Hall effect. Here we report the behavior of magnons in CrI$_3$ under external stimuli, including biaxial uniaxial strain, electric gating, well in-plane out-of-plane magnetic field, revealing that one can thereby tailor states size topology magnonic bandgap. These findings broaden perspective using 2D materials design devices.