Lijun Zhang

Density functional study of FeS, FeSe and FeTe: Electronic structure, magnetism, phonons and superconductivity

We report density functional calculations of the electronic structure, Fermi surface, phonon spectrum, magnetism, and electron-phonon coupling for the superconducting phase FeSe, as well as the related compounds FeS and FeTe. We find that the Fermi-surface structure of these compounds is very similar to that of the Fe-As based superconductors, with cylindrical electron sections at the zone corner, cylindrical hole surface sections, and depending on the compound, other small hole sections at the zone center. As in the Fe-As based materials, these surfaces are separated by a two-dimensional nesting vector at

Electronic correlations in the iron pnictides

(ensuremath{pi},ensuremath{pi})

Density Functional Study of Excess Fe in Fe1+xTe: Magnetism and Doping

. The density of states, nesting, and Fermi-surface size increase, going from FeSe to FeTe. Both FeSe and FeTe show spin-density wave (SDW) ground states, while FeS is close to instability. In a scenario where superconductivity is mediated by spin fluctuations at the SDW nesting vector, the strongest superconductor in this series would be doped FeTe.

Electronic structure localization and spin-state transition in Cu-substituted FeSe: Fe1-xCuxSe

When electrons experience Coulomb repulsion, their kinetic energy becomes significantly reduced. This effect has now been measured in the pnictide superconductor LaFePO, and shows that correlations between electrons in these materials are just as strong as in some copper oxide and ruthenate superconductors. In correlated metals derived from Mott insulators, the motion of an electron is impeded by Coulomb repulsion due to other electrons. This phenomenon causes a substantial reduction in the electron’s kinetic energy, leading to remarkable experimental manifestations in optical spectroscopy1. The high-transition-temperature (Tc) superconducting cuprates are perhaps the most studied examples of such correlated metals. The occurrence of high-Tc superconductivity in the iron pnictides2,3,4 puts a spotlight on the relevance of correlation effects in these materials5. Here, we present an infrared and optical study on single crystals of the iron pnictide superconductor LaFePO. We find clear evidence of electronic correlations in metallic LaFePO with the kinetic energy of the electrons reduced to half of that predicted by band theory of nearly free electrons. We deduce that electronic many-body effects are important in the iron pnictides despite the absence of a Mott transition.

Tuning optical properties of transparent conducting barium stannate by dimensional reduction

The electronic and magnetic properties of the excess Fe in iron telluride

Electronic structure of Ba(Fe,Ru)2As2 and Sr(Fe,Ir)2As2 alloys

{text{Fe}}_{(1+x)}text{Te}

High-pressure Phase Stability and Superconductivity of Pnictogen Hydrides and Chemical Trends for Compressed Hydrides

are studied by density functional calculations. We find that the excess Fe occurs with valence near

Density functional study of the overdoped iron chalcogenide TlFe 2 Se 2 with ThCr 2 Si 2 structure

{text{Fe}}^{+}

Possible Superconductivity in Fe-Sb Based Materials: Density Functional Study of LiFeSb

and thus provides electron doping of approximately one carrier per Fe, and furthermore that the excess Fe is strongly magnetic. Thus it will provide local moments that interact with the plane Fe magnetism, and these are expected to persist in phases where the magnetism of the planes is destroyed, for example, by pressure or doping. The results are discussed in the context of superconductivity.

Electronic structure, magnetism and superconductivity of layered iron compounds

We report density-functional studies of the Fe{sub 1-x}Cu{sub x}Se alloy done using supercell and coherent-potential approximation methods. Magnetic behavior was investigated using the disordered local moment approach. We find that Cu occurs in a nominal d{sup 10} configuration and is highly disruptive to the electronic structure of the Fe sheets. This would be consistent with a metal-insulator transition due to Anderson localization. We further find a strong crossover from a weak moment itinerant system to a local moment magnet at x{approx}0.12. We associate this with the experimentally observed jump near this concentration. our results are consistent with the characterization of this concentration-dependent jump as a transition to a spin glass.