Letter | Published:

Bandgap opening in few-layered monoclinic MoTe2

Nature Physics volume 11, pages 482486 (2015) | Download Citation

Abstract

Layered transition metal dichalcogenides (TMDs) have attracted renewed interest owing to their potential use as two-dimensional components in next-generation devices1,2. Although group 6 TMDs, such as MX2 with M = (Mo, W) and X = (S, Se, Te), can exist in several polymorphs3, most studies have been conducted with the semiconducting hexagonal (2H) phase as other polymorphs often exhibit inhomogeneous formation1,4,5,6. Here, we report a reversible structural phase transition between the hexagonal and stable monoclinic (distorted octahedral or 1T′) phases in bulk single-crystalline MoTe2. Furthermore, an electronic phase transition from semimetallic to semiconducting is shown as 1T′-MoTe2 crystals go from bulk to few-layered. Bulk 1T′-MoTe2 crystals exhibit a maximum carrier mobility of 4,000 cm2 V−1 s−1 and a giant magnetoresistance of 16,000% in a magnetic field of 14 T at 1.8 K. In the few-layered form, 1T′-MoTe2 exhibits a bandgap opening of up to 60 meV, which our density functional theory calculations identify as arising from strong interband spin–orbit coupling. We further clarify that the Peierls distortion is a key mechanism to stabilize the monoclinic structure. This class of semiconducting MoTe2 unlocks the possibility of topological quantum devices based on non-trivial Z2-band-topology quantum spin Hall insulators in monoclinic TMDs (ref. 7).

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Acknowledgements

The authors wish to acknowledge J-H. Kim and S. Adhikari for absorption spectroscopy. This work was supported by the Institute for Basic Science (IBS-R011-D1) in Korea and by the National Research Foundation of Korea (NRF) under Grant No. 2014R1A1A2056386. D-H.C., H-J.S. and K.J.C. were supported by the NRF under Grant No. NRF-2005-0093845. S.W.K. was supported by NRF Grant No. 2013R1A1A1008025.

Author information

Author notes

    • Dong Hoon Keum
    •  & Suyeon Cho

    These authors contributed equally to this work.

Affiliations

  1. IBS Center for Integrated Nanostructure Physics (CINAP), Institute for Basic Science, Sungkyunkwan University, Suwon 440-746, Korea

    • Dong Hoon Keum
    • , Suyeon Cho
    • , Jung Ho Kim
    • , Min Kan
    • , Jae-Yeol Hwang
    • , Sung Wng Kim
    • , Heejun Yang
    •  & Young Hee Lee
  2. Department of Energy Science, Sungkyunkwan University, Suwon 440-746, Korea

    • Dong Hoon Keum
    • , Jung Ho Kim
    • , Min Kan
    • , Haeyong Kang
    • , Jae-Yeol Hwang
    • , Sung Wng Kim
    • , Heejun Yang
    •  & Young Hee Lee
  3. Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon 305-701, Korea

    • Duk-Hyun Choe
    • , Ha-Jun Sung
    •  & K. J. Chang

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Contributions

All authors participated in scientific discussion. D.H.K. acquired the TEM images, and measured the optical absorbance and the Seebeck coefficients. S.C. synthesized single-crystalline 2H- and 1T′-MoTe2, constructed the phase diagram, and measured the Raman spectra, XRD and the SdH oscillation with the giant magnetoresistance. J.H.K. fabricated the devices and measured the temperature-dependent resistivity. H.K. and J-Y.H. assisted with those measurements. D-H.C., H-J.S. and M.K. calculated the electronic structure. S.W.K., H.Y., K.J.C. and Y.H.L. are the principal investigators.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Sung Wng Kim or Heejun Yang or K. J. Chang or Young Hee Lee.

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DOI

https://doi.org/10.1038/nphys3314

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