5,435 research outputs found
Distorted magnetic orders and electronic structures of tetragonal FeSe from first-principles
We use the state-of-the-arts density-functional-theory method to study
various magnetic orders and their effects on the electronic structures of the
FeSe. Our calculated results show that, for the spins of the single Fe layer,
the striped antiferromagnetic orders with distortion are more favorable in
total energy than the checkerboard antiferromagnetic orders with tetragonal
symmetry, which is consistent with known experimental data, and the inter-layer
magnetic interaction is very weak. We investigate the electronic structures and
magnetic property of the distorted phases. We also present our calculated spin
coupling constants and discuss the reduction of the Fe magnetic moment by
quantum many-body effects. These results are useful to understand the
structural, magnetic, and electronic properties of FeSe, and may have some
helpful implications to other FeAs-based materials
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
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
Enhancement in superconducting transition temperature and upper critical field of LaO0.8F0.2FeAs with antimony doping
We report the synthesis and characterization of antimony doped oxypnictide
superconductor, LaO0.8F0.2FeAs1-xSbx (x = 0.05 and 0.10). The parent compound
LaOFeAs with fluorine doping exhibits superconductivity at maximum transition
temperature ~ 28.5 K [11]. Here we partially substitute As by Sb
(LaO0.8F0.2FeAs1-xSbx) and observe enhancement of the transition temperature to
30.1 K. This is the only instance so far where Tc increases with doping in the
conducting layer (FeAs) and this leads to the highest transition temperature in
any La-based oxypnictide. XRD and EDAX measurements confirm phase purity of the
samples and the presence of Sb. The magneto-resistance measurements show that
the value of upper critical field Hc2(0) to be about 73 T corresponding to a
coherence length of 22 angstrom. The Seebeck coefficient measurements indicate
electron transport with strong contribution from electron-electron correlation.
These results provide interesting insight to the origin of superconductivity in
these novel series of compounds
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
Nernst effect of the new iron-based superconductor LaOFFeAs
We report the first Nernst effect measurement on the new iron-based
superconductor LaOFFeAs . In the normal state, the
Nernst signal is negative and very small. Below a large positive peak
caused by vortex motion is observed. The flux flowing regime is quite large
compared to conventional type-II superconductors. However, a clear deviation of
the Nernst signal from normal state background and an anomalous depression of
off-diagonal thermoelectric current in the normal state between and 50
K are observed. We propose that this anomaly in the normal state Nernst effect
could correlate with the SDW fluctuations.Comment: 8 pages, 4 figures; Latex file changed, references adde
Constraints on Spin-Independent Nucleus Scattering with sub-GeV Weakly Interacting Massive Particle Dark Matter from the CDEX-1B Experiment at the China Jin-Ping Laboratory
We report results on the searches of weakly interacting massive particles
(WIMPs) with sub-GeV masses () via WIMP-nucleus spin-independent
scattering with Migdal effect incorporated. Analysis on time-integrated (TI)
and annual modulation (AM) effects on CDEX-1B data are performed, with 737.1
kgday exposure and 160 eVee threshold for TI analysis, and 1107.5
kgday exposure and 250 eVee threshold for AM analysis. The sensitive
windows in are expanded by an order of magnitude to lower DM masses
with Migdal effect incorporated. New limits on at
90\% confidence level are derived as 1010
for TI analysis at 50180 MeV/, and
1010 for AM analysis at
75 MeV/3.0 GeV/.Comment: 5 pages, 4 figure
Spin-singlet superconductivity with multiple gaps in PrO0.89F0.11FeAs
Since the discovery of high transition-temperature (Tc) superconductivity in
copper oxides two decades ago, continuous efforts have been devoted to
searching for similar phenomenon in other compounds. With the exception of MgB2
(Tc =39 K), however, Tc is generally far lower than desired. Recently,
breakthrough has been made in a new class of oxypnictide compounds. Following
the initial discovery of superconductivity in LaO1-x FxFeAs (Tc =26 K), Tc
onset has been raised to 55 K in ReO1-xFxFeAs (Re: Ce, Pr, Nd, Sm). Meanwhile,
unravelling the nature of the energy associated with the formation of
current-carrying pairs (Cooper pairs), referred to as the superconducting
energy gap, is the first and vital step towards understanding why the
superconductivity occurs at such high temperature and is also important for
finding superconductors with still higher Tc. Here we show that, on the basis
of the nuclear magnetic resonance (NMR) measurements in PrO0.89F0.11FeAs (Tc
=45 K), the Cooper pair is in the spin-singlet state (two spins are
anti-paralleled), with two energy gaps opening below Tc. The results strongly
suggest the existence of nodes (zeros) in the gap. None of superconductors
known to date has such unique gap features, although copper-oxides and MgB2
share part of them.Comment: submitted on May 1
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