Strong vibrational coupling in room temperature plasmonic resonators

Abstract

Strong vibrational coupling has been realized in a variety of mechanical systems. However, there have been no experimental observations of strong coupling of the acoustic modes of plasmonic nanostructures, due to rapid energy dissipation in these systems. Here we realized strong vibrational coupling in ultra-high frequency plasmonic nanoresonators by increasing the vibrational quality factors by an order of magnitude. We achieved the highest frequency quality factor products of f × Q = 1.0 × 10 13 Hz for the fundamental mechanical modes, which exceeds the value of 0.6 × 10 13 Hz required for ground state cooling. Avoided crossing was observed between vibrational modes of two plasmonic nanoresonators with a coupling rate of g = 7.5 ± 1.2 GHz, an order of magnitude larger than the dissipation rates. The intermodal strong coupling was consistent with theoretical calculations using a coupled oscillator model. Our results enabled a platform for future observation and control of the quantum behavior of phonon modes in metallic nanoparticles.

Acoustic cavities in 2D heterostructures

“…The physical mechanisms that define the fundamental limits attainable for Q values (i.e., phonon lifetimes) in different 2D materials will be discussed below. While differences in the performance of individual cavities can be 5× (attributed to variability in manual exfoliation), the f × Q product for our MoS 2 devices remains at or above that required for ground state laser cooling ( f × Q = 6 × 10 12 Hz) 30 . Figure 1d, e inset highlight the frequency dependence of energy losses and suggest that the 100–200 GHz frequency range is favorable for maximizing the f × Q product in this measurement geometry at RT.…”

“…The third overtone is then interpreted as ω + (symmetric) mode, while the second overtone is assigned as ω − mode (see refs. 30 , 31 and Supplementary Notes 1 , 6 ). Experimental data for the overtones’ positions in our tri-layer stack are shown by open symbols in Fig.…”

Signatures of Small Morphological Anisotropies in the Plasmonic and Vibrational Responses of Individual Nano-objects

“…34,35 Noticeably, the use of such single-particle approaches allows to shed light onto processes which can hardly be investigated in ensemble measurements, such as the polarization dependence of the optical properties of nano-objects, sensitive to their shape and orientation [36][37][38][39] and the quality factors of their plasmonic and vibrational modes. 8,[40][41][42][43][44][45][46] Quantitative polarization-resolved extinction measurements using spatial modulation spectroscopy enable optical characterization of the dimensions and orientation of simple nano-objects (nanorods and nanospheres) placed in a known environment and, vice versa, to measure the refractive index of the local environment if the morphology of the nanoobject has been previously determined. 29,[39][40][41]47 The present work exploits the assets of single-particle studies to address the impact that slight deviations of a nano-object morphology from an ideal one (here, a perfect cylinder) have on its plasmonic and vibrational responses.…”

Vibrations of Dimers of Mechanically Coupled Nanostructures: Analytical and Numerical Modeling

“…This situation may occur in a variety of systems, differing by the number of nano-objects (e.g., nanoparticle dimer, oligomer or supracrystal) and the nature and strength of their mechanical connections (e.g., via surfactant molecules, a polymer matrix or a supporting solid substrate). [17][18][19][20][21][22][23][24][25][26][27] For metallic nano-objects, such proximity also simultaneously generates plasmonic interactions, which strongly affect their optical response (redshifting for instance the surface plasmon resonances of plasmonic homodimers as compared to those of isolated nanoparticles). [28][29][30][31][32] This effect offers the possibility to selectively probe dimers in optical spectroscopy experiments involving ensembles of nanoparticles, by tuning the light wavelength with a plasmonic resonance generated by plasmonic interactions.…”