10 research outputs found
Possible superconductivity above 25 K in single crystalline Co-doped BaFeAs
We present superconducting properties of single crystalline
Ba(FeCo)As by measuring magnetization, resistivity,
upper critical field, Hall coefficient, and magneto-optical images. The
magnetization measurements reveal fish-tail hysteresis loop at high
temperatures and relatively high critical current density above
A/cm at low temperatures. Upper critical field determined by resistive
transition is anisotropic with anisotropic parameter 3.5. Hall effect
measurements indicate that Ba(FeCo)As is a
multiband system and the mobility of electron is dominant. The magneto-optical
imaging reveals prominent Bean-like penetration of vortices although there is a
slight inhomogeneity in a sample. Moreover, we find a distinct
superconductivity above 25 K, which leads us to speculate that higher
transition temperature can be realized by fine tuning Co-doping level.Comment: 4 pages, 5 figure
Josephson Plasma Resonance in with Spatially Dependent Interlayer-Phase Coherence
We study the Josephson plasma resonance (JPR) in
BiSrCaCuO (BSCCO) with spatially dependent interlayer-phase
coherence (IPC). The half-irradiated BSCCO (HI-BSCCO), in which columnar
defects are introduced only in a half of the sample, shows several resonance
peaks, which are not simple superposition of the peaks in irradiated- and
pristine-parts. JPR in HI-BSCCO changes its character from irradiated- to
pristine-type at a crossover frequency (). We demonstrate that the
one-dimensional \LSGE, which takes into account the spatial dependence of IPC,
can reproduce most of the experimental findings including the presence of
.Comment: 4 figure
Asymmetric Field Profile in Bose Glass Phase of Irradiated YBa2Cu3O7-d: Loss of Interlayer Coherence around 1/3 of Matching Field
Magneto-optical imaging in YBa2Cu3O7-d with tilted columnar defects (CD's)
shows an asymmetric critical-state field profile. The observed hysteretic shift
of the profile ridge (trough) from the center of the sample is explained by
in-plane magnetization originated from vortex alignment along CD's. The
extracted ratio of the in-plane to out-of-plane magnetization component has a
maximum at 1/5 of matching field () and disappears above ,
suggesting a reduction of interlayer coherence well bellow in the Bose
glass phase. Implications are discussed in comparison with the vortex liquid
recoupling observed in irradiated Bi2Sr2CaCu2O8+y.Comment: Revtex, 4 pages, 5 figures, also see a movie at
(http://www.ap6.t.u-tokyo.ac.jp/kitaka/Research/d-line/index_e.htm). This
manuscript will appear in Phys. Rev. Let
Strong 3D correlations in vortex system of Bi2212:Pb
The experimental study of magnetic flux penetration under crossed magnetic
fields in Bi2212:Pb single crystal performed by magnetooptic technique (MO)
reveals remarkable field penetration pattern alteration (flux configuration
change) and superconducting current anisotropy enhancement by the in-plane
field. The anisotropy increases with the temperature rise up to . At an abrupt change in the flux behavior is found; the
correlation between the in-plane magnetic field and the out-of-plane magnetic
flux penetration disappears. No correlation is observed for . The
transition temperature does not depend on the magnetic field strength.
The observed flux penetration anisotropy is considered as an evidence of a
strong 3D - correlation between pancake vortices in different CuO planes at . This enables understanding of a remarkable pinning observed in
Bi2212:Pb at low temperatures.Comment: 8 pages, 9 figure