4,857 research outputs found
Effects of Pressure on the Electronic and Structural Properties of LaOFeAs
We studied the pressure effects on the electronic and structural properties
of LaOFeAs by first-principles calculations. For the anti-ferromagnetic (AFM)
phase with stripe- like aligned Fe spins, the electronic density of states at
the Fermi level (N (EF)) slightly descends first with increasing applied
pressure, then bounces up with further increasing pressure (or decreasing
volume), and reaches its maximum at ~ 29.2 GPa with the volume ~ 80% of the
ambient pressure value (V0). At this volume (V = 0.8V0), the LaOFeAs crystal
undergoes a structural phase transition from the orthorhombic structure to the
tetragonal one, which is accompanied by the disappearance of the long-ranged
AFM order.Comment: 20 pages, 5 figure
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Possible gapless helical edge states in hydrogenated graphene
Electronic band structures in hydrogenated graphene are theoretically
investigated by means of first-principle calculations and an effective
tight-binding model. It is shown that regularly designed hydrogenation to
graphene gives rise to a large band gap about 1 eV. Remarkably, by changing the
spatial pattern of the hydrogenation, topologically distinct states can be
realized, where the topological nontriviality is detected by parity
indices in bulk and confirmed by the existence of gapless edge/interface states
as protected by the mirror and sublattice symmetries. The analysis of the wave
functions reveals that the helical edge states in hydrogenated graphene with
the appropriate design carry pseudospin currents that are reminiscent of the
quantum spin Hall effect. Our work shows the potential of hydrogenated graphene
in pseudospin-based device applications.Comment: 9 pages, 5 figure
Topological electronic states in holey graphyne
We unveil that the holey graphyne (HGY), a two-dimensional carbon allotrope
where benzene rings are connected by two CC bonds fabricated
recently in a bottom-up way, exhibits topological electronic states. Using
first-principles calculations and Wannier tight-binding modeling, we discover a
higher-order topological invariant associated with symmetry of the
material, and show that the resultant corner modes appear in nanoflakes
matching to the structure of precursor reported previously, which are ready for
direct experimental observations. In addition, we find that a band inversion
between emergent -like and -like orbitals gives rise to a nontrivial
topology characterized by invariant protected by an energy gap
as large as 0.52 eV, manifesting helical edge states mimicking those in the
prominent quantum spin Hall effect, which can be accessed experimentally after
hydrogenation in HGY. We hope these findings trigger interests towards
exploring the topological electronic states in HGY and related future
electronics applications.Comment: 19+20 pages, 4+7 figure
Higher-order topology in honeycomb lattice with Y-Kekul\'e distortions
We investigate higher-order topological states in honeycomb lattice with
Y-Kekul\'e distortions that preserve crystalline symmetry. The gapped
states in expanded and shrunken distortions are adiabatically connected to
isolated hexamers and Y-shaped tetramer states, respectively, where the former
possesses nontrivial higher-order topology characterized by a
invariant. Topological corner states exist in a flake structure with expanded
distortion where the hexamers are broken at the corners. Our work reveals that
honeycomb lattice with Y-Kekul\'e distortions serves as a promising platform to
study higher-order topological states.Comment: 5 pages, 3 figure
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