304 research outputs found
Chalcogen-height dependent magnetic interactions and magnetic order switching in FeSeTe
Magnetic properties of iron chalcogenide superconducting materials are
investigated using density functional calculations. We find the stability of
magnetic phases is very sensitive to the height of chalcogen species from the
Fe plane: while FeTe with optimized Te height has the double-stripe-type
magnetic ordering, the single-stripe-type ordering
becomes the ground state phase when Te height is lowered below a critical value
by, e.g., Se doping. This behavior is understood by opposite Te-height
dependences of the superexchange interaction and a longer-range magnetic
interaction mediated by itinerant electrons. We also demonstrate a linear
temperature dependence of the macroscopic magnetic susceptibility in the
single-stripe phase in contrast to a constant behavior in the double-stripe
phase. Our findings provide a comprehensive and unified view to understand the
magnetism in FeSeTe and iron pnictide superconductors.Comment: 4 pages, 4 figure
Graphyne: Hexagonal network of carbon with versatile Dirac cones
We study alpha, beta, and gamma graphyne, a class of graphene allotropes with
carbon triple bonds, using a first-principles density-functional method and
tight-binding calculation. We find that graphyne has versatile Dirac cones and
it is due to remarkable roles of the carbon triple bonds in electronic and
atomic structures. The carbon triple bonds modulate effective hopping matrix
elements and reverse their signs, resulting in Dirac cones with reversed
chirality in alpha graphyne, momentum shift of the Dirac point in beta
graphyne, and switch of the energy gap in gamma graphyne. Furthermore, the
triple bonds provide chemisorption sites of adatoms which can break sublattice
symmetry while preserving planar sp2-bonding networks. These features of
graphyne open new possibilities for electronic applications of carbon-based
two-dimensional materials and derived nanostructures.Comment: 5 pages, 5 figures, 1 tabl
- β¦