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We propose a novel class of two-dimensional (2D) Dirac materials in the MX family (M = Be, Mg, Zn and Cd, X = Cl, Br and I), which exhibit graphene-like band structures with linearly-dispersing Dirac-cone states over large energy scales (0.8-1.8 eV) and ultra-high Fermi velocities comparable to graphene. Spin-orbit coupling opens sizable topological band gaps so that these compounds can be effectively classified as quantum spin Hall insulators. The electronic and topological properties are found to be highly tunable and amenable to modulation via anion-layer substitution and vertical electric field. Electronic structures of several members of the family are shown to host a Van-Hove singularity (VHS) close to the energy of the Dirac node. The enhanced density-of-states associated with these VHSs could provide a mechanism for inducing topological superconductivity. The presence of sizable band gaps, ultra-high carrier mobilities, and small effective masses makes the MX family promising for electronics and spintronics applications.

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Publication history

Received: 12 June 2020
Revised: 28 July 2020
Accepted: 29 July 2020
Published: 01 March 2021
Issue date: March 2021

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© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature

Acknowledgements

The authors would like to thank Tay-Rong Chang and Jiatao Sun for helpful discussions. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, under Award #DE-SC0019275. It benefitted from the supercomputing resources of the National Energy Research Scientific Computing Center (NERSC), a U.S. Department of Energy Office of Science User Facility operated under Contract No. DE-AC02-05CH11231, and Temple University’s HPC resources supported in part by the National Science Foundation through major research instrumentation grant number 1625061 and by the US Army Research Laboratory under contract number W911NF-16-2-0189. S. X. D. and Y.-F. Z. acknowledge support from the National Key Research and Development Program of China (No. 2016YFA0202300), Strategic Priority Research Program (No. XDB30000000), the National Natural Science Foundation of China (No. 61888102), and the International Partnership Program of the Chinese Academy of Sciences (No. 112111KYSB20160061).

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Email: nanores@tup.tsinghua.edu.cn

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