Enhanced Two-Dimensional Exciton Propagation via Strong Light–Matter Coupling with Surface Lattice Plasmons

Abstract

Exciton−polaritons�hybrid exciton−photon quasi-particles�have enabled exciting long-range coherent transport by taking advantage of the properties of their photonic component. However, most experimental demonstrations of strong coupling have been based on semiconductor Fabry−Peŕot microcavities. Here, we report an open and versatile exciton−polariton platform by integrating two-dimensional lead halide perovskites with plasmonic nanoparticle arrays, which support hybridization between excitons and surface lattice resonances in the strong coupling regime. Benefitting from the open architecture, we directly visualized polariton-enhanced exciton transport via angle-dependent transient absorption microscopy measurements. The observed transport enhancement extends into the picosecond timescale, leading to more than 1 order of magnitude improvement of exciton migration, from ∼10 nm to 100s of nanometers. We proposed a polaritonmediated exciton transport model and obtained an average polariton velocity of ∼1 × 10 6 m/s for states with an ∼40% photonic fraction. These results demonstrate plasmonic particle arrays as a versatile and adaptable cavity to enhance exciton transport.

Strong Coupling of Two-Dimensional Excitons and Plasmonic Photonic Crystals: Microscopic Theory Reveals Triplet Spectra

“…In the results Section , we choose the MNP and PC parameters to maximize the optical near-field of the PC, such that both resonances appear for the same frequency range. In this case, the collective interactions do not cause a narrow distinct peak, as focused on, e.g., in refs , , – , but rather amplify and sharpen the present MNP resonance.…”

“…Its distance dependency is depicted in the inset of Figure b, illustrating the (δ z ) −2 proportionality. To assign the hybrids to a particular coupling regime, the effective Rabi energy Ω eff ≠ 0 is compared with the line width γ ex and γ pl of the individual constituents. , A coupling strength leading to a peak splitting that is small compared to the line widths as, e.g., in the δ z = 17 nm , case is still assigned to weak coupling and has been observed in experiments with TMDCs coupled to a MNP or a PC in refs , , , and .…”

Embrace the darkness: An experimental perspective on organic exciton–polaritons

“…This has mostly been demonstrated in steady-state measurements, 119,153,156 though there are limited reports of time-resolved studies focusing on such energy transport in Fabry-P erot cavities, BSWPs, and even cavity-free polaritons. 104,139,147,[157][158][159] Yet, the choice of materials, methods of characterization, and cavity architectures are sufficiently scattered that it remains unclear how to control these effects, and the field is in need of systematic investigations to understand the mechanisms underpinning polariton transport. Numerous steady-state studies have highlighted the potential of polariton-assisted energy transfer, with reported distances reaching up to 100's of micrometers.…”

“…However, a recently published set of time-resolved studies reveals a much more complicated picture. 104,139,147,[157][158][159] In each case, the polariton-assisted energy transport was studied using some variation of pump-probe microscopy (Fig. 12).…”

“…152 Initial studies indicated, however, that the observed transport velocities are orders of magnitude below the expected group velocity and that polariton transport cannot occur through a simple ballistic process. 104,139,147,[157][158][159] In one case, the population was found to expand linearly in time and subsequent analysis suggested that the transport was diffusive in nature [Fig. 13(a)].…”