6,573 research outputs found
LaFeAsOF: A low carrier density superconductor near itinerant magnetism
Density functional studies of 26K superconducting LaFeAs(O,F) are reported.
We find a low carrier density, high density of states, and modest
phonon frequencies relative to . The high leads to proximity to
itinerant magnetism, with competing ferromagnetic and antiferromagnetic
fluctuations and the balance between these controlled by doping level. Thus
LaFeAs(O,F) is in a unique class of high superconductors: high
ionic metals near magnetism.Comment: Shortened published form. Typos correcte
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 2D nesting vector at
(,). The density of states, nesting and Fermi surface size increase
going from FeSe to FeTe. Both FeSe and FeTe show spin density wave ground
states, while FeS is close to an 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.Comment: Added note regarding recent experimental observations of
superconductivity under pressure. Some additional discussio
Possible Superconductivity in Fe-Sb Based Materials: Density Functional Study of LiFeSb
We investigate the electronic and other properties of the hypothetical
compound LiFeSb in relation to superconducting LiFeAs and FeSe using density
functional calculations. The results show that LiFeSb in the LiFeAs structure
would be dynamically stable in the sense of having no unstable phonon modes,
and would have very similar electronic and magnetic properties to the layered
Fe based superconductors. Importantly, a very similar structure for the Fermi
surface and a spin density wave related to but stronger than that in the
corresponding As compound is found. These results are indicative of possible
superconductivity analogous to the Fe-As based compounds if the spin density
wave can be suppressed by doping or other means. Prospects for synthesizing
this material in pure form or in solid solution with FeTe are discussed.Comment: Additional discussion about superconductivity in the Fe materials in
relation to chi(q) and experimental observation
Unconventional sign-reversing superconductivity in LaFeAsO_(1-x)F_x
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
Limits on Light Weakly Interacting Massive Particles from the First 102.8 kg day Data of the CDEX-10 Experiment
We report the first results of a light weakly interacting massive particles
(WIMPs) search from the CDEX-10 experiment with a 10 kg germanium detector
array immersed in liquid nitrogen at the China Jinping Underground Laboratory
with a physics data size of 102.8 kg day. At an analysis threshold of 160 eVee,
improved limits of 8 and 3 cm at a
90\% confidence level on spin-independent and spin-dependent WIMP-nucleon cross
sections, respectively, at a WIMP mass () of 5 GeV/ are
achieved. The lower reach of is extended to 2 GeV/.Comment: 5 pages, 4 figure
Search for Light Weakly-Interacting-Massive-Particle Dark Matter by Annual Modulation Analysis with a Point-Contact Germanium Detector at the China Jinping Underground Laboratory
We present results on light weakly interacting massive particle (WIMP)
searches with annual modulation (AM) analysis on data from a 1-kg mass -type
point-contact germanium detector of the CDEX-1B experiment at the China Jinping
Underground Laboratory. Datasets with a total live time of 3.2 yr within a 4.2
yr span are analyzed with analysis threshold of 250 eVee. Limits on
WIMP-nucleus (-) spin-independent cross sections as function of WIMP
mass () at 90\% confidence level (C.L.) are derived using the dark
matter halo model. Within the context of the standard halo model, the 90\% C.L.
allowed regions implied by the DAMA/LIBRA and CoGeNT AM-based analysis are
excluded at 99.99\% and 98\% C.L., respectively. These results correspond to
the best sensitivity at 6 among WIMP AM
measurements to date.Comment: 5 pages, 4 figure
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