Coherent multipolar amplification of chiroptical scattering and absorption from a magnetoelectric nanoparticle

Background-free detection of inherently weak chiroptical signals remains one of the great challenges in research communities and industries. We demonstrate coherent multipolar amplification of chiroptical responses via a magnetoelectric nanoparticle capped with an optically active monolayer encapsulated in a lossless background medium. Such an achiral nanoparticle can simultaneously support both electric and magnetic Mie-type resonances. We show how the combined excitation of orthogonal multipolar modes of the same order boosts the magnetoelectric coupling induced by the adsorbed chiral molecules, thus enabling coherently enhanced chiroptical responses from the ligand-capped magnetoelectric nanoparticle and allowing for absolute chirality measurements, in comparison with non-magnetoelectric nanoparticles. Furthermore, we develop rigorous expressions to separate relative contributions of chiral and nonchiral portions of circular differential absorption cross section, and analyzed the chirality-dependent far-field radiation patterns at different overlapped multipolar modes, providing a theoretical framework to understand the underlying enhancement mechanism of the magnetoelectric-assisted sensing of molecular chirality. Regular nanoparticles amplify the electric component of the radiating field, yet such amplification is generally insufficient to reveal the inherently weak chiral signal of molecules. By simultaneously exciting magnetic and electric modes of a coreshell magnetoelectric nanoparticle, the authors are able to strongly enhance the chiroptical response of the optically active medium.

Automated summary

This study demonstrates a method for amplifying chiroptical responses using magnetoelectric nanoparticles capped with an optically active monolayer to eliminate background interference. By simultaneously exciting magnetic and electric modes, the magnetoelectric coupling is enhanced, resulting in improved chiroptical responses from the nanoparticles.