Magic-angle magnonic nanocavity in a magnetic moiré superlattice
Jilei Chen, Lang Zeng, Hanchen Wang, M. Madami, G. Gubbiotti, Song Liu, Jianyu Zhang, Zifeng Wang, Wenhao Jiang, Yan Zhang, Dapeng Yu, Jean‐Philippe Ansermet, Haiming Yu
Abstract
Moir\'e superlattices have recently been extensively studied in both electronic and photonic systems, e.g., magic-angle bilayer graphene showing superconductivity and twisted bilayer photonic crystals leading to magic-angle lasers. However, the moir\'e physics is barely studied in the field of magnonics, i.e., in using spin waves for information processing. In this work, we report magnon flat-band formation in twisted bilayer magnonic crystals at the optimal ``magic angle'' and interlayer exchange coupling combination using micromagnetic simulations. At the flat-band frequency, magnons undergo a strong two-dimensional confinement with a lateral scale of about 185 nm. The magic-angle magnonic nanocavity occurs at the $AB$ stacking region of a moir\'e unit cell, unlike its photonic counterpart which is at the $AA$ region, due to the exchange-induced magnon spin torque. The magnon flat band originates from band structure reformation induced by interlayer magnon-magnon coupling. Our results enable efficient accumulation of magnon intensity in a confined region that is key for potential applications such as magnon Bose-Einstein condensation and even magnon lasing.