arXiv subjects

Gregory V. Hartland

Publications and source records attributed to Gregory V. Hartland.

4 recordsLinked to original sources

arXiv2026

Plasmon-Exciton Coupling and Dephasing in Hybrid Au Nanostructure/J-Aggregate Systems

The coupling between propagating surface plasmon polaritons (SPPs) in Au nanostructures and the exciton transitions of cyanine dye J-aggregates has been examined using leakage radiation microscopy. Real space images of the nanostructures give the propagation lengths of the leaky SPP modes, and Fourier space images yield their dispersion curves. The dispersion curves show an avoided crossing when the structures are coated with J-aggregates, with a Rabi splitting of approximately 30 meV. The lifetimes of the coupled states were calculated by combining the measured propagation lengths with the group velocities obtained from the dispersion curves. The lifetimes decrease from ~50 fs for the bare Au nanostructures, to ~10 fs in the avoided crossing region for the coupled J-aggregate/Au nanostructure system. Analytical Holstein-Tavis-Cummings model calculations and finite element simulations of the coupled system show that the decrease in lifetime is primarily due to energy dissipation into dark states associated with the J-aggregates.

physics.chem-ph↗

arXiv2019

Strong Vibrational Coupling in Room Temperature Plasmonic Resonators

Strong vibrational coupling has been realized in a variety of mechanical systems from cavity optomechanics to electromechanics.$^{1, 2, 3, 4, 5}$ It is an essential requirement for enabling quantum control over the vibrational states.$^{6, 7, 8, 9, 10, 11}$ The majority of the mechanical systems that have been studied to date are vibrational resonances of dielectric or semiconductor nanomaterials coupled to optical modes.$^{12, 13, 14, 15}$ While there are fewer studies of coupling between two mechanical modes,$^{3, 9}$ particularly, there have been no experimental observation of strong coupling of the ultra-high frequency acoustic modes of plasmonic nanostructures, due to the 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. This is achieved through blocking an energy dissipation pathway in the form of out-going acoustic waves. We achieved the highest frequency quality factor products of $\mathbf{f}\times\mathbf{Q}=1.0\times10^{13}$ Hz for the fundamental mechanical modes in room temperature plasmonic nanoresonators reported to date, which exceeds the value of $0.1\times10^{13}$ Hz required for ground state cooling. Avoided crossing were observed between the vibrational modes of two plasmonic nanoresonators with a coupling rate of $\mathbf{g}=7.5\pm 1.2$ 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 expanded the strong coupling systems for mechanical resonators and enabled a platform for future observation and control of the quantum behavior of phonon modes in metallic nanoparticles.

physics.app-ph↗

arXiv2017

Understanding Hot-Electron Generation and Plasmon Relaxation in Metal Nanocrystals: Quantum and Classical Mechanisms

Generation of energetic (hot) electrons is an intrinsic property of any plasmonic nanostructure under illumination. Simultaneously, a striking advantage of metal nanocrystals over semiconductors lies in their very large absorption cross sections. Therefore, metal nanostructures with strong and tailored plasmonic resonances are very attractive for photocatalytic applications. However, the central questions regarding plasmonic hot electrons are how to quantify and extract the optically-excited energetic electrons in a nanocrystal. We develop a theory describing the generation rates and the energy-distributions of hot electrons in nanocrystals with various geometries. In our theory, hot electrons are generated owing to surfaces and hot spots. The formalism predicts that large optically-excited nanocrystals show the excitation of mostly low-energy Drude electrons, whereas plasmons in small nanocrystals involve mostly hot electrons. The energy distributions of electrons in an optically-excited nanocrystal show how the quantum many-body state in small particles evolves towards the classical state described by the Drude model when increasing nanocrystal size. We show that the rate of surface decay of plasmons in nanocrystals is directly related to the rate of generation of hot electrons. Based on a detailed many-body theory involving kinetic coefficients, we formulate a simple scheme describing the plasmon's dephasing. In most nanocrystals, the main decay mechanism of a plasmon is the Drude friction-like process and the secondary path comes from generation of hot electrons due to surfaces and electromagnetic hot spots. This latter path strongly depends on the size, shape and material of the nanocrystal, correspondingly affecting its efficiency of hot-electron production. The results in the paper can be used to guide the design of plasmonic nanomaterials for photochemistry and photodetectors.

cond-mat.mes-hall↗

arXiv2017

What's so Hot about Electrons in Metal Nanoparticles?

Metal nanoparticles are excellent light absorbers. The absorption processes create highly excited electron-hole pairs and recently there has been interest in harnessing these hot charge carriers for photocatalysis and solar energy conversion applications. The goal of this Perspectives article is to describe the dynamics and energy distribution of the charge carriers produced by photon absorption, and the implications for the photocatalysis mechanism. We will also discuss how spectroscopy can be used to provide insight into the coupling between plasmons and molecular resonances. In particular, the analysis shows that the choice of material and shape of the nanocrystal can play a crucial role in hot electron generation and coupling between plasmons and molecular transitions. The detection and even calculation of many-body hot-electron processes in the plasmonic systems with continuous spectra of electrons and short lifetimes are challenging, but at the same time very interesting from the point of view of both potential applications and fundamental physics. We propose that developing an understanding of these processes will provide a pathway for improving the efficiency of plasmon-induced photocatalysis.

cond-mat.mes-hall↗