Routing valley exciton emission of a WS2monolayer via delocalized Bloch modes of in-plane inversion-symmetry-broken photonic crystal slabs

The valleys of two-dimensional transition metal dichalcogenides (TMDCs) offer a new degree of freedom for information processing. To take advantage of this valley degree of freedom, on the one hand, it is feasible to control valleys by utilizing different external stimuli, such as optical and electric fields. On the other hand, nanostructures are also used to separate the valleys by near-field coupling. However, for both of the above methods, either the required low-temperature environment or low degree of coherence properties limit their further applications. Here, we demonstrate that all-dielectric photonic crystal (PhC) slabs without in-plane inversion symmetry (C(2)symmetry) can separate and route valley exciton emission of a WS(2)monolayer at room temperature. Coupling with circularly polarized photonic Bloch modes of such PhC slabs, valley photons emitted by a WS(2)monolayer are routed directionally and are efficiently separated in the far field. In addition, far-field emissions are directionally enhanced and have long-distance spatial coherence properties. Separating valleys through photonic crystals A method for separating novel excitonic valley states has been developed by researchers in China using an asymmetric photonic crystal. The emerging field of valleytronics aims to encode information using local minima (valleys) in the electronic band structure of certain materials, especially ultrathin layers of transition metal dichalcogenides (TMDCs). However, it is difficult to separate valley states at any distance from a sample, except at extremely low temperatures. To address this problem, Lei Shi at Fudan University in Shanghai and co-workers deposited a TMDC layer on a photonic crystal, which was etched with triangular holes to break its natural symmetry. The photonic crystal's circularly polarized states interact with the exciton valleys, so that photons from different valley states could be separated far from the sample, even at room temperature.