Fig. 1: Chiral q-BIC metasurface designed for room-temperature valley-selective emission.
a Schematic of the integrated Si-MoSe2 device for controlling spin-photon coupling and generating valley-selective emission (red arrow) at the exciton resonance wavelength of MoSe2 under arbitrarily polarized light excitation at 633 or 640 nm (green arrow). The periodicity (P) of the chiral q-BIC metasurface is 430 nm. PMMA polymethyl methacrylate. b DOPs and Q-factors of some typical heterostructured TMDC-metasurface studies compared to our work. DOP degree of optical circular polarization, R.T. room temperature. Solid squares: achiral metasurfaces; Solid circles: chiral metasurfaces; Blue: low-temperature operation; Red: room-temperature operation. c Simulated transmission spectra of the Jones matrix elements (Trl, Tlr, Tll, and Trr) given the parameters presented in (d) showing a high-Q (677) chiroptical resonance at 772 nm. r represents right-handed circular polarization; l represents left-handed circular polarization. Trl: green solid line; Tlr: red solid line; Tll: blue-green solid line; Trr: black dashed line. (d) Simulated Q-factors versus asymmetry parameter (α). The power-law fit (gray solid line) yields Q ∝ 1/α0.26. e Simulated emission spectra of an ensemble of randomly located and oriented achiral dipoles (number: 200) coupled to the chiral q-BIC mode. Note that the spectra are acquired in the metasurface’s upper space. \({\sigma }^{\pm }\): left-handed (blue solid line) or right-handed (red solid line) circularly polarized emission. f Electric field enhancement distribution for the design of a notched nano-square within a unit cell under LCP (left) and RCP (right) excitation. H = 220 nm, L1 = 130 nm, L2 = 128 nm, W1 = 130 nm, W2 = 152 nm, L = 297 nm. LCP left-handed circular polarization, RCP right-handed circular polarization. g Cross-sectional distribution of normalized OCD atop the chiral metasurface structure at Z = 110 nm and across the structure at X = 0 nm (yz-plane) and Y = 0 nm (xz-plane). OCD optical chirality density. Note that the MoSe2 monolayers are in contact only with the top surface of the structure at Z = 110 nm, rather than occupying the entire internal volume. The origin of the coordinate is at the center of the nanostructure. h Surface-integrated OCD over the xy-plane along the z-axis. The location where the MoSe2 monolayer resides shows a positive surface-integrated OCD. i Top-view (left) and tilted-view (right) scanning electron microscope images of a chiral metasurface. Scale bar: 500 nm.
