EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

The Rabi splitting between the longitudinal plasmons gold nano-bipyramids and the A exciton of monolayer MoS₂ was investigated. This was done at the single particle level and at room temperature. Dark field spectra were correlated with SEM images, revealing the dimensions of the nanoparticles, such as their length, aspect ratio and tip radii. The effects discovered were also demonstrated and confirmed with FDTD simulations. Bipyramids are interesting as nanoresonatorss to achieve strong coupling for a few reasons. Firstly, they exhibit strong electric field confinement at their tips, resulting in a lower resonator mode volume. This increases the overall coupling strength of the system. Larger bipyramids, with a higher electric field confined at their sharp tips, therefore exhibit a stronger coupling with the MoS₂. It was also shown that the bipyramid is the ideal nanoantenna to couple with a transition metal dichalcogenide (TMDC) on a substrate due to the tilt of the plasmon oscillation towards the substrate. This overcomes the misalignment of the electric field and dipole moment, which diminishes the coupling strength for other similar nanoantennae such as nano-cubes or prisms. Bipyramids with lower aspect ratios have a steeper tilt towards the substrate, resulting in a stronger interaction with the MoS₂. The larger bipyramids studied had lower aspect ratios so that the plasmon energy was in resonance with the energy of the A exciton, also resulting in stronger coupling for larger bipyramids. Splitting energies as large as 80 meV were demonstrated, showing a very large coupling strength and confirming that bipyramids are an excellent candidate for achieving strong coupling.