2,021 research outputs found
Angular dependence of resistivity in the superconducting state of NdFeAsOF single crystals
We report the results of angle dependent resistivity of
NdFeAsOF single crystals in the superconducting state. By
doing the scaling of resistivity within the frame of the anisotropic
Ginzburg-Landau theory, it is found that the angle dependent resistivity
measured under different magnetic fields at a certain temperature can be
collapsed onto one curve. As a scaling parameter, the anisotropy can
be determined for different temperatures. It is found that
increases slowly with decreasing temperature, varying from 5.48
at T=50 K to 6.24 at T=44 K. This temperature dependence can be
understood within the picture of multi-band superconductivity.Comment: 7 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
Thermally activated energy and critical magnetic fields of SmFeAsOF
Thermally activated flux flow and vortex glass transition of recently
discovered SmFeAsOF superconductor are studied in magnetic
fields up to 9.0 T. The thermally activated energy is analyzed in two analytic
methods, of which one is conventional and generally used, while the other is
closer to the theoretical description. The thermally activated energy values
determined from both methods are discussed and compared. In addition, several
critical magnetic fields determined from resistivity measurements are presented
and discussed.Comment: Accepted by Superconductor Science and Technolog. 5 page, 4 figure
Superconducting properties of SmO1-xFxFeAs wires with Tc = 52 K prepared by the powder-in-tube method
We demonstrate that Ta sheathed SmO1-xFxFeAs wires were successfully
fabricated by the powder-in-tube (PIT) method for the first time. Structural
analysis by mean of x-ray diffraction shows that the main phase of SmO1-xFxFeAs
was obtained by this synthesis method. The transition temperature of the
SmO0.65F0.35FeAs wires was confirmed to be as high as 52 K. Based on
magnetization measurements, it is found that a globe current can flow on
macroscopic sample dimensions with Jc of ~3.9x10^3 A/cm^2 at 5 K and self
field, while a high Jc about 2x10^5 A/cm^2 is observed within the grains,
suggesting that a significant improvement in the globle Jc is possible. It
should be noted that the Jc exhibits a very weak field dependence behavior.
Furthermore, the upper critical fields (Hc2) determined according to the
Werthamer-Helfand-Hohenberg formula are (T= 0 K) = 120 T, indicating a very
encouraging application of the new superconductors.Comment: 14 pages, 6 figure
Superconductivity at 25 K in hole doped
By partially substituting the tri-valence element La with di-valence element
Sr in , we introduced holes into the system. For the first time, we
successfully synthesized the hole doped new superconductors
. The maximum superconducting transition temperature at
about 25 K was observed at a doping level of x = 0.13. It is evidenced by Hall
effect measurements that the conduction in this type of material is dominated
by hole-like charge carriers, rather than electron-like ones. Together with the
data of the electron doped system , a generic phase diagram
is depicted and is revealed to be similar to that of the cuprate
superconductors.Comment: 5 pages, 5 figure
Point-Contact Spectroscopy of Iron-Based Layered Superconductor LaOFFeAs
We present point-contact spectroscopy data for junctions between a normal
metal and the newly discovered F-doped superconductor
LaOFFeAs (F-LaOFeAs). A zero-bias conductance peak was
observed and its shape and magnitude suggests the presence of Andreev bound
states at the surface of F-LaOFeAs, which provides a possible evidence of an
unconventional pairing symmetry with a nodal gap function. The maximum gap
value meV was determined from the measured spectra,
in good agreement with the recent experiments on specific heat and lower
critical field.Comment: 5 pages, 4 figure
Nuclear magnetic relaxation and superfluid density in Fe-pnictide superconductors: An anisotropic \pm s-wave scenario
We discuss the nuclear magnetic relaxation rate and the superfluid density
with the use of the effective five-band model by Kuroki et al. [Phys. Rev.
Lett. 101, 087004 (2008)] in Fe-based superconductors. We show that a
fully-gapped anisotropic \pm s-wave superconductivity consistently explains
experimental observations. In our phenomenological model, the gaps are assumed
to be anisotropic on the electron-like \beta Fermi surfaces around the M point,
where the maximum of the anisotropic gap is about four times larger than the
minimum.Comment: 10 pages, 8 figures; Submitted versio
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
Point contact Andreev reflection spectroscopy of NdFeAsO_0.85
The newly discovered oxypnictide family of superconductors show very high
critical temperatures of up to 55K. Whilst there is growing evidence that
suggests a nodal order parameter, point contact Andreev reflection spectroscopy
can provide crucial information such as the gap value and possibly the number
of energy gaps involved. For the oxygen deficient NdFeAsO0.85 with a Tc of
45.5K, we show that there is clearly a gap value at 4.2K that is of the order
of 7meV, consistent with previous studies on oxypnictides with lower Tc.
Additionally, taking the spectra as a function of gold tip contact pressure
reveals important changes in the spectra which may be indicative of more
complex physics underlying this structure.Comment: 11 pages, 3 figures. New references included, extra discussion. This
version is accepted in Superconductor Science and Technolog
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