57 research outputs found
Superconductivity at T_c ~ 14 K in Single Crystalline FeTeSe
Single crystalline FeTeSe with a sharp superconducting
transition at 14 K is synthesized via slow furnace
cooling followed by low-temperature annealing. The effect of annealing on the
chemical and superconducting inhomogeneities is carefully characterized. We
also report resistivity, magnetization, and magneto-optical images of this
crystal. Based on the Bean model, critical current density is estimated to
exceed A/cm below 5 K under zero field. Weak fish-tail
effect is identified at lower temperatures.Comment: 4 pages, 4 figure
Transport and magnetic properties of Co-doped BaFe_{2}As_{2} epitaxial thin films
We report resistivity, Hall coefficient, current-voltage characteristics, and
magneto-optical imaging measurements of epitaxial Co-doped BaFe_{2}As_{2} thin
films deposited on MgO(001) substrate. The Hall resistivity of the films has a
substantial contribution arising from anomalous Hall effect of ferromagnetic
components. The critical current density (J_{c}) of the films is ~2 MA/cm^{2}
at low temperatures. Differential magneto-optical images of the remanent state
give similar J_{c} values and also exhibit presence of extended defects in the
film.Comment: 9 pages, 4 figure
Comment on "Isoelectronic Ru substitution at Fe-site in Sm(FeRu)AsOF compound and its effects on structural, superconducting and normal state properties" (arXiv:1004.1978)
Based on the five-orbital model, we derive the reduced impurity scattering
rate in Sm(FeRu)AsOF
from the residual resistivity. At , the transition temperature is
K. For ) the obtained value
of ranges from 1.5 to 2.9, which suggests that the -wave state
cannot survive. We point out that the magnetoresistance frequently gives an
underestimated value of in correlated electron systems.Comment: 2 page
Anisotropic Structure of the Order Parameter in FeSe0.45Te0.55 Revealed by Angle Resolved Specific Heat
The symmetry and structure of the superconducting gap in the Fe-based
superconductors are the central issue for understanding these novel materials.
So far the experimental data and theoretical models have been highly
controversial. Some experiments favor two or more constant or nearly-constant
gaps, others indicate strong anisotropy and yet others suggest gap zeros
("nodes"). Theoretical models also vary, suggesting that the absence or
presence of the nodes depends quantitatively on the model parameters. An
opinion that has gained substantial currency is that the gap structure, unlike
all other known superconductors, including cuprates, may be different in
different compounds within the same family. A unique method for addressing this
issue, one of the very few methods that are bulk and angle-resolved, calls for
measuring the electronic specific heat in a rotating magnetic field, as a
function of field orientation with respect to the crystallographic axes. In
this Communication we present the first such measurement for an Fe-based
high-Tc superconductor (FeBSC). We observed a fourfold oscillation of the
specific heat as a function of the in-plane magnetic field direction, which
allowed us to identify the locations of the gap minima (or nodes) on the Fermi
surface. Our results are consistent with the expectations of an extended s-wave
model with a significant gap anisotropy on the electron pockets and the gap
minima along the \Gamma M (or Fe-Fe bond) direction.Comment: 32 pages, 7 figure
Low-temperature Synthesis of FeTe0.5Se0.5 Polycrystals with a High Transport Critical Current Density
We have prepared high-quality polycrystalline FeTe0.5Se0.5 at temperature as
low as 550{\deg}C. The transport critical current density evaluated by the
current-voltage characteristics is over 700 A/cm2 at 4.2 K under zero field,
which is several times larger than FeTe0.5Se0.5 superconducting wires. The
critical current density estimated from magneto-optical images of flux
penetration is also similar to this value. The upper critical field of the
polycrystalline FeTe0.5Se0.5 at T = 0 K estimated by
Werthamer-Helfand-Hohenberg theory is 585 kOe, which is comparable to that of
single crystals. This study gives some insight into how to improve the
performance of FeTe0.5Se0.5 superconducting wires.Comment: 12 pages, 6 figure
Upper critical field, lower critical field and critical current density of FeTe0.60Se0.40 single crystal
The transport and magnetic studies are performed on high quality
FeTe0.60Se0.40 single crystals to determine the upper critical fields (Hc2),
lower critical field (Hc1) and the Critical current density (Jc). The value of
upper critical field Hc2 are very large, whereas the activation energy as
determined from the slope of the Arrhenius plots are was found to be lower than
that in the FeAs122 superconductor. The lower critical field was determined in
ab direction and c direction of the crystal, and was found to have a anisotropy
of 'gamma'{=(Hc1//c) / (Hc1//b)} ~ 4. The magnetic isotherms measured up to 12
Tesla shows the presence of fishtail behavior. The critical current densities
at 1.8K of the single crystal was found to almost same in both ab and c
direction as 1X105 Amp/cm2 in low field regime.Comment: 9 pages, 6 figure
Specific-heat study of superconducting and normal states in FeSe1-xTex (0.6<=x<=1) single crystals: Strong-coupling superconductivity, strong electron-correlation, and inhomogeneity
The electronic specific heat of as-grown and annealed single-crystals of
FeSe1-xTex (0.6<=x<=1) has been investigated. It has been found that annealed
single-crystals with x=0.6-0.9 exhibit bulk superconductivity with a clear
specific-heat jump at the superconducting (SC) transition temperature, Tc. Both
2Delta_0/kBTc [Delta_0: the SC gap at 0 K estimated using the single-band BCS
s-wave model] and Delta C/(gamma_n-gamma_0)Tc [Delta C$: the specific-heat jump
at Tc, gamma_n: the electronic specific-heat coefficient in the normal state,
gamma_0: the residual electronic specific-heat coefficient at 0 K in the SC
state] are largest in the well-annealed single-crystal with x=0.7, i.e., 4.29
and 2.76, respectively, indicating that the superconductivity is of the strong
coupling. The thermodynamic critical field has also been estimated. gamma_n has
been found to be one order of magnitude larger than those estimated from the
band calculations and increases with increasing x at x=0.6-0.9, which is
surmised to be due to the increase in the electronic effective mass, namely,
the enhancement of the electron correlation. It has been found that there
remains a finite value of gamma_0 in the SC state even in the well-annealed
single-crystals with x=0.8-0.9, suggesting an inhomogeneous electronic state in
real space and/or momentum space.Comment: 22 pages, 1 table, 6 figures, Version 2 has been accepted for
publication in J. Phys. Soc. Jp
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