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Abstract
Tuning the plasmonic response with an external magnetic field is extremely promising to achieve active magnetoplasmonic devices, such as next generation refractometric sensors or tunable optical components. Noble metal nanostructures represent an ideal platform for studying and modeling magnetoplasmonic effects through the interaction of free electrons with external magnetic fields, even though their response is relatively low at the magnetic field intensities commonly applied in standard magneto-optical spectroscopies. Here we demonstrate a large magnetoplasmonic response of silver nanoparticles by performing magnetic circular dichroism spectroscopy at high magnetic fields, revealing a linear response to the magnetic field up to 30 T. The exploitation of such high fields allowed us to probe directly the field-induced splitting of circular plasmonic modes by performing absorption spectra with static circular polarizations, giving direct experimental evidence that the magneto-optical activity of plasmonic nanoparticles arises from the energy shift of field-split circular magnetoplasmonic modes.
Highlights
Modulating the plasmonic resonance with an external tool can boost the performance of plasmon-based sensors and devices, enriching the tunability of light−matter interaction and enabling the detection of ultrasmall changes occurring near the surface of the plasmonic nanostructures.[1,2] To this aim, the use of external magnetic fields is extremely promising.[3]
We demonstrate direct field-induced shift of plasmonic modes using a static circular polarization at 30 T, achieving an excellent agreement with standard magnetooptical spectroscopic techniques based on phase-sensitive detection
Such a spectral line shape indicates that light with opposite helicity excites a circular plasmonic mode that is oppositely shifted in energy by an applied field perpendicular to the plane of the plasmonic oscillation, as predicted by the model previously developed for Au NPs, based on Lorentz force evaluation.[11,13]
Summary
Modulating the plasmonic resonance with an external tool can boost the performance of plasmon-based sensors and devices, enriching the tunability of light−matter interaction and enabling the detection of ultrasmall changes occurring near the surface of the plasmonic nanostructures.[1,2] To this aim, the use of external magnetic fields is extremely promising.[3]. The interaction of a magnetic field with free electrons in nanostructures can be modeled accurately on the basis of Lorentz forces acting on such charge carriers, whose motion is triggered by electric field of light and is perturbed by the external magnetic field. Such perturbation splits circular plasmonic modes, which can be selectively addressed with light of opposite helicity using magneto-optical techniques. Such techniques take advantage of polarization modulation and phase-sensitive detection to reveal the relatively weak shift (
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