Fig. 4: Experimental measurement of PL spectra and valley polarization in momentum space.

a–d σ+ and σ− PL intensity distribution in momentum space at 615 nm (upper) and 628 nm (lower). These are for the WS2 monolayer on the PhC slab without in-plane inversion symmetry. e, f Images of valley polarization P(k) in momentum space. The maximum calculated P reaches 88%