Direct Observation of Worm-Like Nanochannels and Emergent Magnon Motifs in Artificial Ferromagnetic Quasicrystals

Quasicrystalline structures and aperiodic metamaterials find applications ranging from established consumer gadgets to potential high-tech photonic components owing to both complex arrangements of constituents and exotic rotational symmetries. Magnonics is an evolving branch of magnetism research where information is transported via magnetization oscillations (magnons). Their control and manipulation are so far best accomplished in periodic metamaterials which exhibit properties artificially modulated on the nanoscale. They give rise to functional components, such as band stop filters, magnonic transistors and nanograting couplers. Here, spin-wave excitations in artificial ferromagnetic quasicrystals created via aperiodic arrangement of nanoholes are studied experimentally. Their ten-fold rotational symmetry results in multiplexed magnonic nanochannels, suggesting a width down to 50 nm inside a so-called Conway worm. Key elements of design are emergent magnon motifs and the worm-like features which are scale-invariant and not present in the periodic metamaterials. By imaging wavefronts in quasicrystals, insight is gained into how the discovered features materialize as a dense wavelength division multiplexer.