Mao-Hua Du

Unconventional Superconductivity with a Sign Reversal in the Order Parameter of LaFeAsO1-xFx

We argue that the newly discovered superconductivity in a nearly magnetic, Fe-based layered compound is unconventional and mediated by antiferromagnetic spin fluctuations, though different from the usual superexchange and specific to this compound. This resulting state is an example of extended s-wave pairing with a sign reversal of the order parameter between different Fermi surface sheets. The main role of doping in this scenario is to lower the density of states and suppress the pair-breaking ferromagnetic fluctuations.

Density Functional Study of LaFeAsO 1 − x F x : A Low Carrier Density Superconductor Near Itinerant Magnetism

Density functional studies of 26 K superconducting LaFeAs(O,F) are reported. We find a low carrier density, high density of states, N(E(F)), and modest phonon frequencies relative to T(c). The high N(E(F)) leads to proximity to itinerant magnetism, with competing ferromagnetic and antiferromagnetic fluctuations and the balance between these controlled by the doping level. Thus LaFeAs(O,F) is in a unique class of high T(c) superconductors: high N(E(F)) ionic metals near magnetism.

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

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

(\ensuremath{\pi},\ensuremath{\pi})

Trapped-dopant model of doping in semiconductor nanocrystals.

. 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.

Enhanced Born charge and proximity to ferroelectricity in thallium halides

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

Energy transport and scintillation of cerium doped elpasolite Cs2LiYCl6: Hybrid functional calculations

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

What causes high resistivity in CdTe

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

First-Principles Study of Native Defects in TlBr: Carrier Trapping, Compensation, and Polarization Phemomenon

{\text{Fe}}^{+}

Native defects and oxygen and hydrogen-related defect complexes in CdTe: Density functional calculations

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.