Strong Dipole-Quadrupole-Exciton Coupling Realized in a Gold Nanorod Dimer Placed on a Two-Dimensional Material

Abstract

Simple systems in which strong coupling of different excitations can be easily realized are highly important, not only for fundamental research but also for practical applications. Here, we proposed a T-shaped gold nanorod (GNR) dimer composed of a long GNR and a short GNR perpendicular to each other and revealed that the dark quadrupole mode of the long GNR can be activated by utilizing the dipole mode excited in the short GNR. It was found that the strong coupling between the dipole and quadrupole modes can be achieved by exciting the T-shaped GNR dimer with a plane wave. Then, we demonstrated the realization of strong dipole–quadrupole–exciton coupling by placing a T-shaped GNR on a tungsten disulfide (WS2) monolayer, which leads to a Rabi splitting as large as ~299 meV. It was confirmed that the simulation results can be well fitted by using a Hamiltonian based on the coupled harmonic oscillator model and the coupling strengths for dipole–quadrupole, dipole–exciton and quadrupole–exciton can be extracted from the fitting results. Our findings open new horizons for realizing strong plasmon–exciton coupling in simple systems and pave the way for constructing novel plasmonic devices for practical applications.

Optical Introduction and Manipulation of Plasmon–Exciton–Trion Coupling in a Si/WS2/Au Nanocavity

“…Moreover, trions consisting of two electrons and one hole can be generated at high laser powers, ,, offering us the opportunity for studying plasmon–trion and even plasmon–exciton–trion coupling in the hybrid nanocavity. Recently, strong coupling among three excitations has become the focus of many studies in light–matter interaction. , In most cases, the strong coupling occurs among two optical/plasmon modes and one exciton resonance. − In comparison, one plasmon mode and two exciton resonances are involved in plasmon–exciton–trion coupling, which enables the energy exchange between excitons and trions mediated by the plasmon mode. Previously, plasmon–exciton–trion coupling was observed in a WS 2 monolayer coupled with an silver nanoprism at a low temperature of 6.0 K .…”

Ultra-confined Propagating Exciton–Plasmon Polaritons Enabled by Cavity-Free Strong Coupling: Beating Plasmonic Trade-Offs

“…As a model system for theoretical investigation, a WS 2 -clad Ag MNW is selected, in which the permittivities of WS 2 ( ε WS2 ) and Ag ( ε Ag ) are described by a Lorentz oscillator model [ 25 ] and an effective Drude model [ 37 ], respectively (see supporting information for details). The thickness of the WS 2 layer is assumed to be 1 nm [ 12 ]. For simplicity and facilitating strong coupling, we only focus on the coupling of excitons to the fundamental mode in the Ag MNW, since the fundamental mode is more confined than the other order ones [ 35 , 38 ], and the single-mode operation is favorable and can be readily realized in many applications [ 32 , 33 , 35 , 39 ].…”

“…Generally, in the plasmonic-TMD system, the key for achieving strong coupling is to ensure a sufficiently large coupling strength that overcomes the overall damping of the coupled system. And a common strategy is to utilize tightly confined cavity modes or localized surface plasmon resonances (LSPRs), which have been previously realized by introducing plasmonic cavities or resonators including metallic F-P cavities [ 8 ], periodic structures [ 9 – 11 ], plasmonic dimers [ 12 , 13 ], single nanoparticles [ 14 – 18 ], and nanogap resonators formed by nanoparticle-over-mirror configurations [ 19 – 21 ]. However, the requisite cavity/resonator may introduce extra complexities [ 22 , 23 ] and challenges for flexible mode engineering [ 24 ], on-chip integration [ 25 ], and remote exciton–polariton transportations [ 26 ] for waveguiding applications.…”

Small mode volume topological photonic states in one-dimensional lattices with dipole--quadrupole interactions

“…Strong dipole-quadrupole coupling can be realized in plasmonic meta-atoms such as H-like nanostructures [51], T-shaped heterodimers [52], and nanorod dimer [53]. For simplicity, we consider homogeneous spherical nanoparticles with radius r. We assume the permittivity of the nanoparticle is described by the Drude model…”