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Two-dimensional topological materials are ideal candidates for low-dissipation electronic devices due to their non-dissipative edge states. As a typical two-dimensional system, graphene is theoretically predicted to exhibit the quantum spin Hall effect under the spin-orbit coupling interaction. However, the band gap in graphene is only in the order of micro-electron volt, which seriously restricts its practical applications. In this work, based on the first-principles calculations, we investigate the electronic structures and topological properties of strained Zr2C12, which is formed by substitutional doping graphene with the group ⅣB 4d transition metal Zr. The phonon spectrum calculation confirms that the freestanding Zr2C12 exhibits excellent dynamic stability. When the spin-orbit coupling is excluded, the bands cross linearly at the K point near the Fermi level, indicating the Dirac semimetal phase of freestanding Zr2C12. The Fermi velocity of the Dirac point is 0.677 × 106 m/s, which is approximately two-thirds of that in graphene (~ 1.00 × 106 m/s). When the spin-orbit coupling is considered, the Dirac point opens a gap of 4.09 meV, which is three orders of magnitude higher than that of undoped graphene. The parity analysis reveals that the Z2 topological invariant of the freestanding Zr2C12 is 1, indicating the system transits into a two-dimensional topological insulator. We also study the properties of Zr2C12 under strain regulation. The calculation results show that the system remains dynamically stable over a wide strain range of -5% to 6%. When the spin-orbit coupling is absent, the conduction band energy at the Γ point continuously rises with increasing strain, and the system maintains the Dirac semimetal phase. After including the spin-orbit coupling, the system remains the nontrivial topological insulator phase over a wide strain range of -5% to 6%, showing robust topological properties. The band gap at the Dirac point first decreases and then increases with increasing strain. When applying -1.6% compression strain, this band gap decreases to the minimum value of 0.059 meV. When the strain further increases to 6%, this gap increases to the maximum value of 8.41 meV. The edge states calculations of Zr2C12 under 6% expansion strain show that the gapless edge states connect the conduction bands and the valence bands, which further verify the non-trivial topological properties of this system under strain regulation. This study expands the research on transition-metal-doped graphene systems, providing a good material platform for further study of low-dissipation electronic devices and quantum computing and communication.
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Keywords:
- graphene /
- doping /
- strain /
- Dirac semimetal /
- quantum spin Hall insulator
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