We have synthesized a monolayer 1T-NbSe2 on bilayer graphene by molecular-beam-epitaxy method and investigated its electronic states by angle-resolved photoemission spectroscopy. In contrast to metallic 2H-NbSe2, monolayer 1T-NbSe2 was found to show insulating characteristics with a finite energy gap and strong modulation of density of states with
periodicity. This suggests the Mott-insulating ground state of monolayer 1T-NbSe2 with the formation of ‘star of David’ clusters. We also found that 1T and 2H phases are selectively fabricated by simply controlling the substrate temperature during epitaxy. The present result opens a pathway toward the crystal-phase engineering based with transition-metal dichalcogenides.
- Yuki Nakata
- Katsuaki Sugawara
- Takashi Takahashi