Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
Optical signature of symmetry variations and spin-valley coupling in atomically thin tungsten dichalcogenides
We report systematic optical studies of WS2 and WSe2 monolayers and multilayers. The efficiency of second harmonic generation shows a dramatic even-odd oscillation with the number of layers, consistent with the presence (absence) of inversion symmetry in even-layer (odd-layer). Photoluminescence (PL) measurements show the crossover from an indirect band gap …