4 research outputs found

    Chern Insulator and Chern Half-Metal States in the Two-Dimensional Spin-Gapless Semiconductor Mn<sub>2</sub>C<sub>6</sub>S<sub>12</sub>

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    Two-dimensional metal–organic frameworks (2D-MOFs) with exotic electronic structures are drawing increasing attention. Here, using first-principles calculations, we demonstrate a spin-gapless MOF, namely, Mn<sub>2</sub>C<sub>6</sub>S<sub>12</sub>, with the coexistence of a spin-polarized Dirac cone and parabolic degenerate points. The Curie temperature evaluated from Monte Carlo simulations implies Mn<sub>2</sub>C<sub>6</sub>S<sub>12</sub> possessing stable ferromagnetism at room temperature. Taking the spin–orbit coupling into account, the Dirac cone is gapped and the degenerate points are lifted, giving rise to multiple topologically nontrivial states with nonzero Chern number, which imply the possibility of Mn<sub>2</sub>C<sub>6</sub>S<sub>12</sub> to be a Chern insulator and a Chern half-metal. Our results offer versatile platforms for achieving spin filtering or a quantum anomalous Hall effect with promising application in spintronics devices

    Dipole Orientation Dependent Symmetry Reduction of Chloroaluminum Phthalocyanine on Cu(111)

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    We demonstrate a dipole orientation dependent symmetry reduction of 4-fold symmetric chloroaluminum phthalocyanine (ClAlPc) molecules on a Cu(111) surface by combined low temperature scanning tunneling microscopy (LT-STM) and density functional theory (DFT) calculations. Unexpected symmetry reduction from 4-fold (C4) to 2-fold (C2) was observed for Cl-down (dipole up) adsorbed ClAlPc, while molecules adopted Cl-up (dipole down) configuration reserved the C4 symmetry. DFT calculations indicated strong charge accumulation at the interface region between Cu surface and the Cl atom in Cl-down adsorbed ClAlPc due to the electron transfer from the bonded Cu atoms. This can result in charge redistribution within the phthalocyanine (Pc) macrocycle, and the formation of anionic Pc with an uptake of 1.3 e, which can be subjected to Jahn–Teller distortion. The inequivalent charge distribution onto the four lobes would be further enlarged due to the conformational distortion. The two down-bended lobes with more electrons interact stronger with the substrate and are much closer to the surface, leading to the C2 symmetry with one pair of up-bended lobes brighter and longer than their perpendicular counterparts for Cl-down adsorbed ClAlPc

    Growth Intermediates for CVD Graphene on Cu(111): Carbon Clusters and Defective Graphene

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    Graphene growth on metal films via chemical vapor deposition (CVD) represents one of the most promising methods for graphene production. The realization of the wafer scale production of single crystalline graphene films requires an atomic scale understanding of the growth mechanism and the growth intermediates of CVD graphene on metal films. Here, we use <i>in situ</i> low-temperature scanning tunneling microscopy (LT-STM) to reveal the graphene growth intermediates at different stages via thermal decomposition of methane on Cu(111). We clearly demonstrate that various carbon clusters, including carbon dimers, carbon rectangles, and ‘zigzag’ and ‘armchair’-like carbon chains, are the actual growth intermediates prior to the graphene formation. Upon the saturation of these carbon clusters, they can transform into defective graphene possessing pseudoperiodic corrugations and vacancies. These vacancy-defects can only be effectively healed in the presence of methane via high temperature annealing at 800 °C and result in the formation of vacancy-free monolayer graphene on Cu(111)

    Kane Fermion in a Two-Dimensional π‑Conjugated Bis(iminothiolato)nickel Monolayer

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    Massless Kane fermions revealed in zinc-blende semiconductors have recently gained interest in the broad study of relativistic materials. In particular, two-dimensional (2D) Kane fermions were expected to be hybrids of pseudospin-1 and -1/2 Dirac fermions. Based on first-principles calculations, we demonstrated that 2D Kane fermions can be realized in a recently synthesized metal–organic framework, namely, bis­(iminothiolato)nickel monolayer. A slight compression takes the system from a semimetal to a semiconductor. At the critical strain of ∼1%, the upper and lower conical bands linearize and touch at a single point intersecting a flat band, showing the same dispersion as the pseudospin-1 Dirac–Weyl systems. We adopted a tight-binding Hamiltonian of a line-centered honeycomb lattice to reveal the origins and topology of the electronic band structure. The coexistence of Kane-type and Dirac-type spectra in the bis­(iminothiolato)nickel monolayer is expected to benefit the study of multi quasiparticle effects
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