Twisted Magnon Frequency Comb and Penrose Superradiance

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 OAMquantum 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 particles 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.