1,678 research outputs found
Strong-coupling superconductivity in layered nickel-based LaOFNiAs
A series of layered nickel-based LaOFNiAs compounds with x=0 to
0.15 are synthesized by solid state reactions. The pure LaONiAs exhibits bulk
superconductivity with Tc 2.75 K. Partial substitution of oxygen by
fluorine increases the transition temperature to K. The
LaOFNiAs sample shows a sharp superconducting transition and a
sharp specific heat jump at the critical temperature. The magnitude of the
specific heat jump is much larger than that expected from the weak-coupling BCS
theory, indicating that this superconductor is in the strong coupling regime.
Furthermore, the temperature dependence of the specific heat deviates strongly
from the theoretical result for the single-band s- or d-wave superconductor,
but shows some character of a multi-gap system.Comment: 4 pages, 4 figure
Superconducting properties of Fe-based layered superconductor LaOFFeAs
We have employed a new route to synthesize single phase F-doped LaOFeAs
compound and confirmed the superconductivity above 20 K in this Fe-based
system. We show that the new superconductor has a rather high upper critical
field of about 54 T. A clear signature of superconducting gap opening below
T was observed in the far-infrared reflectance spectra, with
23.5-4.2. Furthermore, we show that the new
superconductor has electron-type conducting carrier with a rather low carrier
density.Comment: 4 pages, 5 figures, Phys. Rev. Lett. (accepted
Superconductivity at 53.5 K in GdFeAsO1-delta
Here we report the fabrication and superconductivity of the iron-based
arsenic-oxide GdFeAsO1-delta compound with oxygen-deficiency, which has an
onset resistivity transition temperature at 53.5 K. This material has a same
crystal structure as the newly discovered high-Tc ReFeAsO1-delta family (Re =
rare earth metal) and a further reduced crystal lattice, while the Tc starts to
decrease compared with the SmFeAsO1-delta system
Pressure Effect on the superconducting properties of LaO_{1-x}F_{x}FeAs(x=0.11) superconductor
Diamagnetic susceptibility measurements under high hydrostatic pressure (up
to 1.03 GPa) were carried out on the newly discovered Fe-based superconductor
LaO_{1-x}F_{x}FeAs(x=0.11). The transition temperature T_c, defined as the
point at the maximum slope of superconducting transition, was enhanced almost
linearly by hydrostatic pressure, yielding a dT_c/dP of about 1.2 K/GPa.
Differential diamagnetic susceptibility curves indicate that the underlying
superconducting state is complicated. It is suggested that pressure plays an
important role on pushing low T_c superconducting phase toward the main
(optimal) superconducting phase.Comment: 7 pages, 4 figure
Measurement of the branching fractions of psi(2S) -> 3(pi+pi-) and J/psi -> 2(pi+pi-)
Using data samples collected at sqrt(s) = 3.686GeV and 3.650GeV by the BESII
detector at the BEPC, the branching fraction of psi(2S) -> 3(pi+pi-) is
measured to be [4.83 +- 0.38(stat) +- 0.69(syst)] x 10^-4, and the relative
branching fraction of J/psi -> 2(pi+pi-) to that of J/psi -> mu+mu- is measured
to be [5.86 +- 0.19(stat) +- 0.39(syst)]% via psi(2S) -> (pi+pi-)J/psi, J/psi
-> 2(pi+pi-). The electromagnetic form factor of 3(pi+pi-) is determined to be
0.21 +- 0.02 and 0.20 +- 0.01 at sqrt(s) = 3.686GeV and 3.650GeV, respectively.Comment: 17pages, 7 figures, submitted to Phys. Rev.
Electron-hole Asymmetry and Quantum Critical Point in Hole-doped BaFeAs
We show, from first-principles calculations, that the hole-doped side of
FeAs-based compounds is different from its electron-doped counterparts. The
electron side is characterized as Fermi surface nesting, and SDW-to-NM quantum
critical point (QCP) is realized by doping. For the hole-doped side, on the
other hand, orbital-selective partial orbital ordering develops together with
checkboard antiferromagnetic (AF) ordering without lattice distortion. A unique
SDW-to-AF QCP is achieved, and = criteria (in the approximate
J_1&J_2 model) is satisfied. The observed superconductivity is located in the
vicinity of QCP for both sides.Comment: 4 page
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