Magnetic control of light polarization exploiting dark plasmons of magnetoplasmonic nanocavities

CIC nanoGUNE Seminars

Mario Zapata-Herrera, Nanomagnetism Group
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Magnetic control of light polarization exploiting dark  plasmons of magnetoplasmonic nanocavities Magneto-optical effects are widely used in studying technologically relevant magnetic materials as well as to realize optical devices exploiting non- reciprocal propagation of light. The rapidly developing field of magnetoplasmonics merges the concepts from plasmonics and magneto-optics to realize novel phenomena and functionalities for the manipulation of light at the nanoscale.[1] Owing to the intertwined optical and magneto-optical properties, magnetoplasmonics may offer a smart toolbox for actively tunable optical ultrathin surfaces and metasurfaces.[2,3] Enhancing magneto-optical effects is crucial for size reduction of key photonic devices based on non-reciprocal propagation of light and to enable active nanophotonics. In this talk, I will show an approach that exploits dark plasmons to achieve an unprecedented amplification of magneto-optical activity.[4] Our group designed and realized a symmetry broken non-concentric magnetoplasmonic-disk/plasmonic-ring nanocavity fabricated by e-beam lithography. The nanocavity is made of a ferromagnetic disk-shaped nanoantenna precisely placed inside a ring-shaped gold nanoresonator. The broken symmetry enables the free-space light excitation of dark multipolar modes in the plasmonic-nanoring and their hybridization with the dipolar plasmonic resonance of the magnetoplasmonic nanoantenna. Such hybridization gives rise to a multipolar Fano resonance that, when excited, produces a large amplification of the magneto-optic response of the nanocavity, which is ~1-order of magnitude higher than the ordinary amplification provided by localized plasmons in a bare magnetoplasmonics nanoantenna. Such large amplification is explained as due to the peculiar and enhanced electrodynamics of the nanocavity, yielding a large magnetically activated radiant magneto- optical dipole driven by the low-radiant multipolar Fano resonance mode. The concept proposed is general and offers prospects for even higher enhancements via optimization of the nanocavity design. Altogether, our results open a new and fresh path that can revitalize the research and the applications of magnetoplasmonics to active nanophotonics and flat optics. [1] N. Maccaferri et al., Phys. Rev. Lett. **111** , 167401 (2013). [2] K. Lodewijks et al., Nano Lett. **14** , 7207 (2014). [3] I. Zubritskaya et al., Nano Lett. **18** , 302 (2018). [4] A López-Ortega et al. arXiv preprint: arXiv:1903.08392 (2019).