Fig. 7

a (i) Schematic diagram illustrating the coupling between BSW at the surface of the stack and in-plane excitons in the monolayer WS\(_2\). (ii) Experimental dispersion observed in the PL spectrum. (iii) Time-resolved image capturing the propagation of BSW polaritons. (iv) PL intensity plot demonstrating nonlinear power-dependence. b (i) Illustration of the nanocircuit enabling the direction routing of K and K\(^{\prime }\) valley-dependent emission from the WS₂ monolayer. (ii) Numerical simulations depicting gap waveguide modes, showcasing the principle of valley preservation. (iii) Two-photon photoluminescence (TPL) images of the valley router when excited by a focused pump laser with \(\sigma +\) or \(\sigma\)- polarization. (iv) TPL spectra measured from ports A and B for \(\sigma +\) or \(\sigma\)- polarized excitations. c (i) The topological polaritonic system comprising a monolayer WS₂ strongly coupled to a nontrivial photonic crystal. (ii) Angle-resolved PL spectra of the helical interface polaritons with \(\sigma +\) and \(\sigma\)- polarized light emissions at the domain wall. (iii) Real-space image capturing the propagation of helical polaritons along the topological domain wall with \(\sigma +\) and \(\sigma\)- excitation. (iv) Spectral and spatial characterization of the helicity of interface polariton propagation, with the color scale representing the degree of helicity. a Reproduced with permission [98]. Copyright [2018] Springer Nature. b Reproduced with permission [99]. Copyright [2022] Springer Nature. c Reproduced with permission [100]. Copyright [2020] AAAS