9,667 research outputs found
Superconductivity at 43 K in Samarium-arsenide Oxides
Since the discovery of high-transition temperature () superconductivity
in layered copper oxides, extensive efforts have been devoted to explore the
higher superconductivity. However, the higher than 40 K can be
obtained only in the copper oxide superconductors so far. The highest reported
value of for non-copper-oxide bulk superconductivity is 39 K in
.\cite{jun} The of about 40 K is close to or above the theoretical
value predicted from BCS theory.\cite{mcmillan} Therefore, it is very
significant to search for non-copper oxide superconductor with the transition
temperature higher than 40 K to understand the mechanism of high-
superconductivity. Here we report the discovery of bulk superconductivity in
samarium-arsenide oxides with ZrCuAiAs type structure.
Resistivity and magnetization measurements show strong evidences for transition
temperature as high as 43 K. is the first non-copper oxide
superconductor with higher than 40 K. The higher than 40 K may be a
strong argument to consider as an unconventional
superconductor.Comment: 8 pages, 4 figure
Superconductivity induced by oxygen deficiency in Sr-doped LaOFeAs
We synthesized Sr-doped sample with single phase,
and systematically studied the effect of oxygen deficiency in the Sr-doped
LaOFeAs system. It is found that substitution of Sr for La indeed induces the
hole carrier evidenced by positive thermoelectric power (TEP), but no bulk
superconductivity is observed. The superconductivity can be realized by
annealing the as-grown sample in vacuum to produce the oxygen deficiency. With
increasing the oxygen deficiency, the superconducting transition temperature
() increases and maximum reaches about 26 K the same as that in
La(O,F)FeAs. TEP dramatically changes from positive to negative in the
nonsuperconducting as-grown sample to the superconducting samples with oxygen
deficiency. While is always negative for all samples (even for Sr-doped
as grown sample). It suggests that the is
still electron-type superconductor.Comment: 4 pages, 4 figure
Transport properties and superconductivity in (M=La and K) with double FeAs layers
We synthesized the samples (M=La and K) with
-type structure. These samples were systematically characterized by
resistivity, thermoelectic power (TEP) and Hall coefficient ().
shows an anomaly in resistivity at about 140 K. Substitution of La
for Ba leads to a shift of the anomaly to low temperature, but no
superconducting transition is observed. Potassium doping leads to suppression
of the anomaly in resistivity and induces superconductivity at 38 K as reported
by Rotter et al.\cite{rotter}. The Hall coefficient and TEP measurements
indicate that the TEP is negative for and La-doped ,
indicating n-type carrier; while potassium doping leads to change of the sign
in and TEP. It definitely indicates p-type carrier in superconducting
with double FeAs layers, being in contrast to the case of
with single FeAs layer. A similar superconductivity is also
observed in the sample with nominal composition .Comment: 4 pages, 4 figure
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
Growth and characterization of A_{1-x}K_xFe_2As_2 (A = Ba, Sr) single crystals with x=0 - 0.4
Single crystals of AKFeAs (A=Ba, Sr) with high quality
have been grown successfully by FeAs self-flux method. The samples have sizes
up to 4 mm with flat and shiny surfaces. The X-ray diffraction patterns suggest
that they have high crystalline quality and c-axis orientation. The
non-superconducting crystals show a spin-density-wave (SDW) instability at
about 173 K and 135 K for Sr-based and Ba-based compound, respectively. After
doping K as the hole dopant into the BaFeAs system, the SDW transition
is smeared, and superconducting samples with the compound of
BaKFeAs (0 0.4) are obtained. The
superconductors characterized by AC susceptibility and resistivity measurements
exhibit very sharp superconducting transition at about 36 K, 32 K, 27 K and 23
K for x= 0.40,0.28,0.25 and 0.23, respectively.Comment: 9 pages, 6 figures, 1 table. This paper together with new data are
modified into a new pape
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
Measurement of \psip Radiative Decays
Using 14 million psi(2S) events accumulated at the BESII detector, we report
first measurements of branching fractions or upper limits for psi(2S) decays
into gamma ppbar, gamma 2(pi^+pi^-), gamma K_s K^-pi^++c.c., gamma K^+ K^-
pi^+pi^-, gamma K^{*0} K^- pi^+ +c.c., gamma K^{*0}\bar K^{*0}, gamma pi^+pi^-
p pbar, gamma 2(K^+K^-), gamma 3(pi^+pi^-), and gamma 2(pi^+pi^-)K^+K^- with
the invariant mass of hadrons below 2.9GeV/c^2. We also report branching
fractions of psi(2S) decays into 2(pi^+pi^-) pi^0, omega pi^+pi^-, omega
f_2(1270), b_1^\pm pi^\mp, and pi^0 2(pi^+pi^-) K^+K^-.Comment: 5 pages, 4 figure
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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