Abstract
Quasicrystals are aperiodically ordered structures with unconventional rotational symmetry. Their peculiar features have been explored in photonics to engineer bandgaps for light waves. Magnons (spin waves) are collective spin excitations in magnetically ordered materials enabling non-charge-based information transmission in nanoscale devices. Here, we report on a two-dimensional magnonic quasicrystal formed by aperiodically arranged nanotroughs in ferrimagnetic yttrium iron garnet. By phase-resolved spin wave imaging at gigahertz frequencies, multidirectional emission from a microwave antenna is evidenced, allowing for a quasicontinuous radial magnon distribution, not observed in reference measurements on a periodic magnonic crystal. We observe partial forbidden gaps, which are consistent with analytical calculations and indicate band formation as well as a modified magnon density of states due to backfolding at pseudo-Brillouin zone boundaries. The findings promise as-desired filters and magnonic waveguides reaching out in a multitude of directions of the aperiodic lattice.
Highlights
Since the discovery of quasicrystals over three and a half decades ago [1], their aperiodicity and unconventional rotational symmetries combined with long-range order have baffled physicists and material scientists alike
We first present Brillouin light scattering (BLS) microscopy performed on the aperiodic Penrose P3 lattice (Fig. 1) and a reference periodic lattice (Fig. 2)
BLS data were taken near the coplanar waveguides (CPWs) by which we excited spin waves (SWs), and an in-plane magnetic field H was applied parallel to the CPW and along the symmetry axis (x axis) of P3-magnonic quasicrystals (MQCs)
Summary
Since the discovery of quasicrystals over three and a half decades ago [1], their aperiodicity and unconventional rotational symmetries combined with long-range order have baffled physicists and material scientists alike. The prime examples of this approach are the studies on artificial photonic crystals and plasmonic crystals [3, 4] based on the 10-fold rotational symmetric Penrose tiling—a two-dimensional (2D) analogue of 3D quasicrystals [5, 6]. The bicomponent MQCs based on a Fibonacci sequence (1D) and Penrose tiling (2D) exhibited a multilevel structure of magnonic bandgaps in simulations [11, 13] These gaps and SW propagation in 1D quasicrystals were evidenced using Brillouin light scattering (BLS) and x-ray microscopy techniques [14, 15]. The reprogrammability of artificial quasicrystals [10, 14, 16] promised a data writing process This makes the study of MQCs timely from the perspective of nanomagnonics, which is an evolving branch in magnetism exploring SWs [17]. Magnon-based logic circuits are expected to transfer and process information efficiently [18]
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