We have fabricated a high-quality monolayer WSe2 film on bilayer graphene by epitaxial growth, and revealed the electronic states by spin- and angle-resolved photoemission spectroscopy. We observed a direct energy gap at the Brillounin-zone corner in contrast to the indirect nature of gap in bulk WSe2, which is attributed to the lack of interlayer interaction and the breaking of space-inversion symmetry in monolayer film. A giant spin splitting of ~0.5 eV, which is the largest among known monolayer transition-metal dichalcogenides, is observed in the energy band around the zone corner. The present results suggest a high potential applicability of WSe2 to develop advanced devices based with the coupling of spin- and valley-degrees of freedom.
@article{arxiv.1508.01249,
title = {Spin- and valley- coupled electronic states in monolayer WSe2 on bilayer graphene},
author = {K. Sugawara and T. Sato and Y. Tanaka and S. Souma and T. Takahashi},
journal= {arXiv preprint arXiv:1508.01249},
year = {2015}
}