Emulating 2D Materials with Magnons

TL;DR

This paper demonstrates that patterned magnonic crystals can emulate the band structure of 2D materials like graphene, enabling tunable topological states and valley physics at accessible frequencies.

Contribution

It introduces a simple 9-band tight-binding model to describe magnonic band structures mimicking 2D materials, facilitating new control over magnonic states and topological phenomena.

Findings

Magnonic band structure resembles graphene with kagome features and flat bands.

Band-gap engineering and topological magnons are achievable at 1D phase boundaries.

Access to valley degrees of freedom via magnonic quantum valley-Hall effect.

Abstract

Spin waves (magnons) in 2D materials have received increasing interest due to their unique states and potential for tunability. However, many interesting features of these systems, including Dirac points and topological states, occur at high frequencies, where experimental probes are limited. Here, we study a crystal formed by patterning a hexagonal array of holes in a perpendicularly magnetized thin film. Through simulation, we find that the magnonic band structure imitates that of graphene, but additionally has some kagome-like character and includes a few flat bands. Surprisingly, its nature can be understood using a 9-band tight-binding Hamiltonian. This clear analogy to 2D materials enables band-gap engineering in 2D, topological magnons along 1D phase boundaries, and spectrally isolated modes at 0D point defects. Interestingly, the 1D phase boundaries allow access to the valley degree of freedom through a magnonic analog of the quantum valley-Hall insulator. These approaches can be extended to other magnonic systems, but are potentially more general due to the simplicity of the model, which resembles existing results from electron, phonon, photon, and cold atom systems. This finding brings the physics of spin waves in 2D materials to more experimentally accessible scales, augments it, and outlines a few principles for controlling magnonic states.