Cavity Quantum Materials

Graphene-based photonic structures have emerged as fertile ground for the controlled manipulation of surface plasmon polaritons (SPPs), providing a two-dimensional platform with low optoelectronic losses. In principle, nanostructuring graphene can enable further confinement of nanolight─enhancing light-matter interactions in the form of SPP cavity modes. In this study, we engineer nanoscale plasmonic cavities composed of self-assembled C₆₀ arrays on graphene. Using scattering-type scanning near-field optical microscopy (s-SNOM) in conjunction with first-principles density functional theory (DFT) calculations, we show that C₆₀ assemblies behave as molecular plasmonic cavities, giving rise to precisely defined hole-doped regions within continuous samples of graphene. By tuning the deposition conditions of C₆₀, the lateral dimensions of molecular cavities can be tailored to the SPP wavelength. Finite-element simulations verify the existence of SPP cavity modes, revealing a real-space pattern characteristic of confined SPPs. Thus, our study provides a straightforward scheme for tailoring SPP mode volume by leveraging molecular self-assembly.

Atomically layered van der Waals (vdW) materials exhibit remarkable properties, including highly confined infrared waveguide modes and the capacity for infrared emission in the monolayer limit. Here we engineered structures that leverage both of these nano-optical functionalities. Specifically, we encased a photoluminescing atomic sheet of MoTe₂ within two bulk crystals of WSe₂, forming a vdW waveguide for the embedded light-emitting monolayer. The modified electromagnetic environment offered by the WSe₂ waveguide alters MoTe₂ spontaneous emission—a phenomenon we directly image with our interferometric nano-photoluminescence technique. We captured spatially oscillating nanoscale patterns prompted by spontaneous emission from MoTe₂ into waveguide modes of WSe₂ slabs. We quantify the resulting Purcell-enhanced emission rate within the framework of a waveguide quantum electrodynamics model, relating the MoTe₂ spontaneous emission rate to the measured waveguide dispersion. Our work marks a substantial advance in the implementation of all-vdW quantum electrodynamics waveguides.