Geoffrey Diederich
Geoffrey M. Diederich1, Mai Nguyen2, John Cenker2, Jordan Fonseca2, Sinabu Pumulo2, Youn Jue Bae3, Daniel G. Chica4, Xavier Roy4, Xiaoyang Zhu4, Di Xiao2, Yafei Ren5, Xiaodong Xu2
1 University of Maryland Baltimore County, 21250 Maryland, USA
2 University of Washington, 98195 Washington, USA
2 Cornell University, 14853 New York, USA
2 Columbia University, 10027 New York, USA
2 University of Delaware, 19716 Delaware, USA
The nonlinear dynamics of collective excitations offer both intriguing fundamental phenomena and significant practical applications. A prime illustration is the field of nonlinear optics, where diverse frequency mixing processes are central to advancing photonic technology. Demonstration of these frequency mixing processes in magnons holds considerable potential for practical applications in magnonics, an emerging frontier of spintronics and an important platform for developing quantum transducers and wave-based computing beyond traditional paradigms. While perturbative nonlinear interactions in magnons have been shown, the non-perturbative regime of magnon nonlinearity has only been accessed under very specifically engineered circumstances. Further, coupling of these nonlinear magnons to a semiconductor exciton, which would greatly extend the feasibility of nonlinear magnonics in hybrid quantum systems, has never been demonstrated to our knowledge. In this talk, I will present an extension to our previous works on the van der Waals semiconducting magnet CrSBr that extends the exciton-magnon coupling into the nonlinear magnon regime. I will show how we can employ transient optical reflectivity to probe the exciton resonance and its magnon-modulated frequency shift, providing access to magnon sidebands in the frequency domain. In the resulting magnon spectra, we see replicas of the fundamental magnon sideband at integer multiples of the magnon frequency produced by nonlinear magnons. I will then show how we can leverage a symmetry-breaking magnetic field to couple the two distinct magnon modes, inducing the appearance of sum- and difference-frequency generation (SFG & DFG) of the magnon modes in our spectra. Further, by selecting a field orientation that brings the DFG mode into resonance with one of the fundamental modes, I will show how we can induce parametric magnon amplification. Finally, I will demonstrate that we can enter the non-perturbative nonlinear magnon regime by presenting results that show high harmonic magnon generation spanning over 20 harmonic orders of exciton-coupled magnons. These results show that CrSBr is an excellent candidate system for exploring the fundamental nonlinear physics of magnons. Further, they provide a path forward to implementing nonlinear magnonics into hybrid quantum systems by leveraging the coupling between magnons and excitons in CrSBr.