Demonstration of valley spin devices by coupling 2D semiconductors to chiral photonic crystal nanocavities

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Based on our simulation results, we have fabricated H1 photonic crystal (PhC) cavities with silicon and characterized their optical characteristics by measuring the photoluminescence (PL) from the cavity. From our measurement results, the cavity resonant wavelengths and quality factor are consistent with our numerical simulations. In principle, the H1 PhC cavity has two degenerate dipole modes. However, as fabrication errors are avoidable, the spectral degeneracy of the modes are lifted resulting in the observation of two peaks in the PL spectra. The magnitude of the peak splitting varies from cavity to cavity. Results from our current sample will be used as feedback for our next fabrication in order to reduce fabrication error and thus improve the mode degeneracies.On the other hand, we intend to heterogeneously integrate 2D van der Waals material on the photonic crystal. We have further developed the technologies related to 2D materials. In particular, we carried out 2D materials exfoliation and transfer using combinations of polydimethylsiloxane (PDMS), anthracene and hexagonal boron nitride (hBN) flakes.We also developed a novel type of photonic crystal cavity, namely the 2D material-induced nanocavity in a photonic crystal waveguide. A 2D material flake of a suitable width can provide a small local refractive index modulation to induce the formation of a cavity in a PhC waveguide at wherever the 2D material is placed. We confirmed the feasibility of such method by FDTD and FEM simulations.