Abstract
In this work sharp silver nanotips are analyzed and proposed as useful plasmonic tools to reduce the threshold for the onset of strong coupling in the electromagnetic interaction of a point-like emitter with localized surface plasmons. If compared to similarly-sized spherical nanoparticles, conically-shaped nanoparticles turn out to be extremely useful to reduce the oscillator strength requirements for the emitting dipole, a reduction of the threshold by one sixth being obtained in a double cone configuration. Moreover the transition to the strong coupling regime is analyzed for several cone apertures, revealing a nonmonotonic behavior with the appearance of an optimal cone geometry. The emitted-light spectrum is obtained from the computation of the perturbative decay rate and photonic Lamb shift in the classical framework of the Discrete Dipole Approximation. This combined classical-quantum electrodynamics treatment is useful for the theoretical investigation on nonperturbative light-matter interactions involving complex shaped nanoparticles or aggregates.
Highlights
In the study of the spontaneous emission of light by an excited dipolar emitter, several different regimes can be recognized [1]
For simplicity, that the peaks are of Lorentzian lineshape, the spectrum in Eq (1) can be worked out analytically and it is found that the threshold condition for the onset of a vacuum Rabi splitting is [16] γ < 4 f Γmax, where γ and Γmax are the full width at half maximum and the maximum height of the peak, respectively, this being due to the linear dependence of the total decay rate on f
We have numerically predicted the onset of strong electromagnetic coupling for low oscillator strength dipole emitters put in proximity of sharp silver nanotips. 20 nm Ag cones, either in a single or double configuration, turn out to be much more advantageous with respect to a 20 nm diameter Ag sphere, if an optimal aperture is selected
Summary
In the study of the spontaneous emission of light by an excited dipolar emitter, several different regimes can be recognized [1]. The strong coupling regime can be entered when the interaction of the emitter with radiation is significantly increased due to photonic density localization and enhancement phenomena For this reason, localized surface plasmons of metal nanosystems represent promising candidates for the investigation of strong coupling effects, thanks to the possibility of concentrating optical energy on the sub-wavelength scale and to enhance the local density of states of radiation, producing an increase of the spontaneous decay rate sometimes comparable with high-Q optical cavities. Our computational results reveal the possibility to enter the strong coupling regime with a dipole oscillator strength as low as a few units for the double cone configuration, a value which is compatible with those of organic molecules or quantum dots It represents one of the lowest thresholds in the current literature [10, 11, 13,14,15, 17]. Combining the computational DDA method with a quantum electrodynamical treatment of radiation-matter interaction results in a powerful approach, that can be applied to nanoparticles of any shape and for any given dispersive dielectric function
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
