Quasi free-standing silicene in a superlattice with hexagonal boron nitride.
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In particular, the Dirac cone of silicene is preserved.Due to the wide band gap of hexagonal boron nitride, the superlattice realizes the characteristic physical phenomena of free-standing silicene.In particular, we address by model calculations the combined effect of the intrinsic spin-orbit coupling and an external electric field, which induces a transition from a semimetal to a topological insulator and further to a band insulator.
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Affiliation: Physical Science & Engineering Division, KAUST, Thuwal 23955-6900, Kingdom of Saudi Arabia.
ABSTRACT
We study a superlattice of silicene and hexagonal boron nitride by first principles calculations and demonstrate that the interaction between the layers of the superlattice is very small. As a consequence, quasi free-standing silicene is realized in this superlattice. In particular, the Dirac cone of silicene is preserved. Due to the wide band gap of hexagonal boron nitride, the superlattice realizes the characteristic physical phenomena of free-standing silicene. In particular, we address by model calculations the combined effect of the intrinsic spin-orbit coupling and an external electric field, which induces a transition from a semimetal to a topological insulator and further to a band insulator. No MeSH data available. |
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Mentions: The presence of a Dirac cone has been claimed for silicene grown on metallic substrate but there is still an ongoing discussion about the validity of this claim13141517. Because of the large band gap of hexagonal boron nitride, we do not expect B or N states in the vicinity of the Fermi level in the case of our superlattice, so that the situation is much less involved. The band structure obtained from our calculations is shown in Fig. 2. We observe indeed a well preserved Dirac cone with a SOC gap of 1.6 meV. Analysis of the partial densities of states (not shown) clearly demonstrates that the Dirac cone traces back to the pz orbitals of the Si atoms, while contributions of the B and N atoms are found above 0.6 eV and below −1.0 eV only, with respect to the Fermi energy. We note that the observed Dirac cone is slightly shifted such that the Dirac point does not fall exactly on the Fermi energy. It appears at an energy of about 0.04 eV, i.e., the silicene is slightly hole doped. The energetical shift of the Dirac cone can be attributed to a tiny charge transfer between the silicene and the hexagonal boron nitride. Quantitative analysis shows that the silicene layer loses 0.06 electrons per 8 atoms. However, besides this small effect (which can be overcome by a minute doping), the charactersitics of the silicene Dirac cone are perfectly maintained in a superlattice with hexagonal boron nitride. In the following we will therefore study the effect of an external electric field on free-standing silicene to describe the properties of the superlattice. In Ref. 4 the role of the intrinsic SOC and external electric field for the opening of a band gap have been discussed. The electric field breaks the sublattice symmetry, which induces a finite band gap. The intrinsic SOC has the same effect. Our calculations (for an ideal buckling of 0.46 Å) show that the SOC (Ez = 0) on its own results in a band gap of 1.6 meV, which is consistent with the previously reported value in Ref. 4. To obtain the same gap by an electric field (without SOC) a value of Ez = 11.2 meV/Å is needed, see Fig. 3(a). |
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Affiliation: Physical Science & Engineering Division, KAUST, Thuwal 23955-6900, Kingdom of Saudi Arabia.
No MeSH data available.