Photonic Spin Hall Effect Modified by Ultrathin Au Films and Monolayer Transition Metal Dichalcogenides in One-Dimensional Photonic Crystal

When the metal film becomes far thinner than the electron mean free path (EMFP) in their bulk counterpart, many exotic optical properties accompanied with numbers of novel applications may emerge. Herein, the photonic spin Hall effect (PSHE) occurring on the surface of one-dimensional photonic crystal consisting of ultrathin Au films, monolayer transition metal dichalcogenides (TMDCs), and one defective layer is investigated. The Au film thickness ranges from 2.4 to 40 nm which covers the thickness range below the EMFP (37.7 nm) in bulk Au. Results show that ultrathin Au films are more competent to enhance the PSHE than bulk Au film. In particular, the maximum spin-dependent transverse displacement (37.94 times of the incident wavelength) at the Au film thickness of 4.4 nm is more than 12-fold higher than that at the bulk Au film with thickness of 40 nm. Besides it may be due to the coupling between the short-range surface plasmon polaritons and the B excitonic resonance in monolayer WS2, among four monolayer TMDCs (i.e., MoS2, MoSe2, WS2, WSe2), the photonic crystal with monolayer WS2 gives the strongest PSHE. Additionally, evolutions of photonic spin Hall shifts with the refractive index of defective layer, incident wavelength, and incident angle are also studied in detail. These findings shed light on the superiority of ultrathin metal films for light manipulation in spinoptics and may provide new routes to tailor the optical helicity in nanophotonic devices.