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>
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)
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
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
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,
bisÂ(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 bisÂ(iminothiolato)nickel monolayer
is expected to benefit the study of multi quasiparticle effects