Twisted Magnon Frequency Comb and Penrose Superradiance

TL;DR

This paper explores the nonlinear interactions in ferromagnetic nanodisks, revealing a twisted magnon frequency comb and demonstrating magnonic Penrose superradiance, with potential applications in generating high-OAM twisted magnons.

Contribution

It introduces the concept of twisted magnon frequency combs and demonstrates magnonic Penrose superradiance in ferromagnetic nanodisks, revealing new quantum effects in magnon-vortex interactions.

Findings

The mode spacing of the tMFC equals the vortex core gyration frequency.

Adjacent spectral lines differ by one OAM quantum number.

Higher-order modes are amplified while lower-order modes are trapped.

Abstract

Quantization effects of the nonlinear magnon-vortex interaction in ferromagnetic nanodisks are studied. We show that the circular geometry twists the spin-wave fields with spiral phase dislocations carrying quantized orbital angular momentum (OAM). Meanwhile, the confluence and splitting scattering of twisted magnons off the gyrating vortex core (VC) generates a frequency comb consisting of discrete and equally spaced spectral lines, dubbed as twisted magnon frequency comb (tMFC). It is found that the mode spacing of the tMFC is equal to the gyration frequency of the VC and the OAM quantum numbers between adjacent spectral lines differ by one. By applying a magnetic field perpendicular to the plane of a thick nanodisk, we observe a magnonic Penrose superradiance inside the cone vortex state, which mimics the amplification of waves scattered from a rotating black hole. It is demonstrated that the higher-order modes of tMFC are significantly amplified while the lower-order ones are trapped within the VC gyrating orbit which manifests as the ergoregion. These results suggest a promising way to generate twisted magnons with large OAM and to drastically improve the flatness of the magnon comb.