Ultra-High Q Nanobeam Cavities for 2D Heterostructures

In this talk, I will describe our recent investigations of the heterogeneous integration of 2D materials onto novel Si₃N₄ nanobeam optical cavities [1-5]. These nanobeam optical resonators host ultra-high cavity modes and allow us to explore novel light-matter and multimodal vibronic – phonon – photon couplings mediated by electronic excitations. For hBN-encapsulated MoS₂monolayers, we observe a nonmonotonic temperature dependence of the cavity-trion interaction strength, consistent with the nonlocal light-matter interactions in which the extent of the centre-of-mass wave function is comparable to the cavity mode volume in space[1]. For MoSe₂ homo-bilayers [2], we study the twist-dependent moiré coupling. For small angles, we find a pronounced redshift of the K−K and Γ−K excitons, an effect that we trace to the underlying moiré pattern. Studies of thick hBN layers coupled to the high-Q nanocavity modes reveal intriguing dynamics: For example, we identify the zero-phonon line transition of charged boron vacancies () [3,4] and observe a novel tripartite coupling between the cavity photonic modes, lattice phonon and nanobeam vibrational modes. The fingerprint for this tripartite coupling is a pronounced asymmetry in the emission spectrum for cavities with a Q-factor above a threshold of ~10⁴. Similar asymmetries are not observed for cavities without centers, or lower Q-cavities. To explain our findings, we model the system with phonon-induced light-matter coupling and compare it to the Jaynes-Cummings model for usual emitters. Our results reveal that the multipartite interplay arises during the light-matter coupling of centers, illustrating that it is phonon-induced, rather than caused by the thermal population of phonon modes. Our results indicate how different photon ( emission, cavity photonic) and phonon ( phonon, cavity mechanical) modes provide a novel system to interface spin defects, photons, and phonons in condensed matter systems.

[1] C. Qian et al. Phys. Rev. Lett. 128, 237403 (2022)
[2] V. Villafane et al. Phys. Rev. Lett. 130, 026901, (2022)
[3] C. Qian et al. Phys. Rev. Lett. 130, 126901 (2023)
[4] C. Qian et al. Nano Lett, 22, 13, 5137–5142, (2022)
[5] R. Rizzato et al. Nat. Comm. 14, 5089, (2023)