Odd-even layer-number effect of valence-band spin splitting in WTe2

When a crystal becomes thin to the atomic level, peculiar phenomena discretely depending on its layer numbers (n) start to appear. Here, we investigate the electronic band dispersions of multilayer WTe2 (2-5 layers), by performing laser-based microfocused angle-resolved photoelectron spectroscopy on exfoliated flakes sorted by n. We observe that the holelike valence bands start to cross the Fermi level when the number of layers is increased from 2- to 3 layers, which should be related to the insulator-semimetal transition, as well as the 30-70-meV spin splitting of valence bands manifesting in even n as a signature of stronger structural asymmetry. Our result fully demonstrates the possibility of the large energy-scale band and spin manipulation through the finite-n stacking procedure.