Spin-Wave Frequency Comb and Penrose Superradiance

An optical frequency comb consists of a set of discrete and equally spaced frequencies and has found wide applications in the synthesis over a broad range of spectral frequencies of electromagnetic waves and precise optical frequency metrology. Here, we investigate quantization effects of the nonlinear magnon-vortex interaction in ferromagnetic nanodisks. 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 particles scattered from a rotating black hole.