Original Article

Citation: NPG Asia Materials (2016) 8, e321; doi:10.1038/am.2016.157
Published online 4 November 2016

Monolayer 1T-NbSe2 as a Mott insulator

Yuki Nakata1, Katsuaki Sugawara2, Ryota Shimizu2,3, Yoshinori Okada2, Patrick Han2, Taro Hitosugi2,3, Keiji Ueno4, Takafumi Sato1 and Takashi Takahashi1,2

  1. 1Department of Physics, Tohoku University, Sendai, Japan
  2. 2WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Sendai, Japan
  3. 3Department of Applied Chemistry, Tokyo Institute of Technology, Tokyo, Japan
  4. 4Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama, Japan

Correspondence: Dr K Sugawara, WPI Research Center, Advanced Institute for Materials Research, Tohoku University, Katahira 2-1-1, Aoba-ku, Miyagi, Sendai 980-8577, Japan. E-mail: k.sugawara@arpes.phys.tohoku.ac.jp

Received 13 May 2016; Revised 29 July 2016; Accepted 20 August 2016



The emergence of exotic quantum phenomena is often triggered by a subtle change in the crystal phase. Transition metal dichalcogenides (TMDs) exhibit a wide variety of novel properties, depending on their crystal phases, which can be trigonal prismatic (2H) or octahedral (1T). Bulk NbSe2 crystallizes into the 2H phase, and the charge density wave and the superconductivity emerge simultaneously and interact with each other, thereby creating various anomalous properties. However, these properties and their interplay in another polymorph, 1T-NbSe2, have remained unclear because of the difficulty of synthesizing it. Here we report the first experimental realization of a monolayer 1T-NbSe2 crystal grown epitaxially on bilayer graphene. In contrast with 2H-NbSe2, monolayer 1T-NbSe2 was found to be a Mott insulator, with an energy gap of 0.4eV. We also found that the insulating 1T and metallic 2H phases can be selectively fabricated by simply controlling the substrate temperature during epitaxy. The present results open a path to crystal-phase engineering based on TMDs.

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