109 research outputs found
Hidden robust presence of a hole Fermi surface in a heavily electron doped iron based superconductor LaFeAs
We investigate the electronic structure of a recently discovered, heavily
electron-doped iron based superconductor LaFeAs. Although first
principles calculation shows apparent absence of hole Fermi surfaces around the
point, we reveal, by hypothetically removing the La orbital
contribution, that a hole Fermi surface around the point is
essentially present. In the collapsed phase of LaFeAs, which is
non-superconducting, the hole Fermi surface is found to be absent, and the
difference from the uncollapsed superconducting phase can be naturally
understood within the spin-fluctuation mediated pairing scenario.Comment: 6 pages, 4 figure
Minimum model and its theoretical analysis for superconducting materials with BiS layers
We perform first principles band calculation of the newly discovered
superconductor LaOFBiS, and study the lattice structure and the
fluorine doping dependence of the gap between the valence and conduction bands.
We find that the distance between La and S as well as the fluorine doping
significantly affects the band gap. On the other hand, the four orbital model
of the BiS layer shows that the lattice structure does not affect this
portion of the band. Still, the band gap can affect the carrier concentration
in the case of light electron doping, which in turn should affect the transport
properties.Comment: submitted as Proc. ISS2012, 4 pages, 4 figure
Maximizing Fermi surface multiplicity optimizes superconductivity in iron pnictides
We study the condition for optimizing superconductivity in the iron pnictides
from the lattice structure point of view. Studying the band structure of the
hypothetical lattice structure of LaFeAsO, the hole Fermi surface multiplicity
is found to be maximized around the Fe-As-Fe bond angle regime where the
arsenic atoms form a regular tetrahedron. Superconductivity is optimized within
this three hole Fermi surface regime, while the stoner factor of the
antiferromagnetism has an overall tendency of increasing upon decreasing the
bond angle. Combining also the effect of the varying the Fe-As bond length, we
provide a guiding principle for obtaining high .Comment: 5 pages, 3 figure
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