290 research outputs found
Collective pinning of imperfect vortex lattices by material line defects in extreme type-II superconductors
The critical current density shown by a superconductor at the extreme type-II
limit is predicted to follow an inverse square-root power law with external
magnetic field if the vortex lattice is weakly pinned by material line defects.
It acquires an additional inverse dependence with thickness along the line
direction once pinning of the interstitial vortex lines by material point
defects is included. Moderate quantitative agreement with the critical current
density shown by second-generation wires of high-temperature superconductors in
kG magnetic fields is achieved at liquid-nitrogen temperature.Comment: 10 pages, 3 figures, 2 tables. To appear in Physical Review
Thin film growth by pulsed laser deposition and properties of 122-type iron-based superconductor AE(Fe1--xCox)2As2 (AE = alkaline earth)
This paper reports comprehensive results on thin-film growth of 122-type
iron-pnictide superconductors, AE(Fe1-xCox)2As2 (AE = Ca, Sr, and Ba,
AEFe2As2:Co) by a pulsed laser deposition method using a neodymium-doped
yttrium aluminum garnet laser as an excitation source. The most critical
parameter to produce the SrFe2As2:Co and BaFe2As2:Co phases is the substrate
temperature (Ts). It is difficult to produce highly-pure CaFe2As2:Co phase thin
film at any Ts. For BaFe2As2:Co epitaxial films, controlling Ts at 800-850
{\deg}C and growth rate to 2.8-3.3 {\AA}/s produced high-quality films with
good crystallinity, flat surfaces, and high critical current densities > 1
MA/cm2, which were obtained for film thicknesses from 100 to 500 nm. The doping
concentration x was optimized for Ba(Fe1-xCox)2As2 epitaxial films, leading to
the highest critical temperature of 25.5 K in the epitaxial films with the
nominal x = 0.075.Comment: will be published in the special issue of Superconductor Science and
Technology, `Iron12
Strong Enhancement of the Critical Current at the Antiferromagnetic Transition in ErNi2B2C Single Crystals
We report on transport and magnetization measurements of the critical current
density Jc in ErNi2B2C single crystals that show strongly enhanced vortex
pinning at the Neel temperature TN and low applied fields. The height of the
observed Jc peak decreases with increasing magnetic field in clear contrast
with that of the peak effect found at the upper critical field. We also
performed the first angular transport measurements of Jc ever conducted on this
compound. They reveal the correlated nature of this pinning enhancement, which
we attribute to the formation of antiphase boundaries at TN.Comment: 3 figure
Comment on `Strong Vortex Liquid Correlation' from Multiterminal Measurements on Untwinned YBaCuO Single Crystals'
A.Rydh and \"O.Rapp [Phys. Rev. Lett. {\bf 86}, 1873 (2001).] claim that the
vortex liquid in untwinned YBaCuO crystals is correlated
above the melting transition, in striking contrast to previous work [D.L\'opez
{\it et al.}, Phys. Rev. Lett. {\bf 76}, 4034 (1996).]. In this Comment we
present new measurements using the same experimental technique on twinned and
untwinned YBaCuO crystals with similar overall
characteristics as those reported by Rydh and Rapp . The comparison of the
vortex correlation response in both cases indicates that the central conclusion
of their work is not correct. Our results reconfirm the work by L\'opez {\it et
al.} and points on the origin of the misinterpretation in the work of Rydh and
Rapp.Comment: comment on A.Rydh and \"O.Rapp, Phys. Rev. Lett. {\bf 86}, 1873
(2001). accepted in Phys. Rev. Let
Upper critical field and thermally activated flux flow in single crystalline TlRbFeSe
The upper critical field of
TlRbFeSe single crystals has been determined by
means of measuring the electrical resistivity in both a pulsed magnetic field
(60T) and a DC magnetic field (14T). It is found that
linearly increases with decreasing temperature for ,
reaching T. On the
other hand, a larger with a strong convex curvature
is observed for ((18K)60T). This compound shows a moderate anisotropy of the upper
critical field around , but decreases with decreasing temperature.
Analysis of the upper critical field based on the Werthamer-Helfand-Hohenberg
(WHH) method indicates that is orbitally limited for
, but the effect of spin paramagnetism may play an
important role on the pair breaking for . All these
experimental observations remarkably resemble those of the iron pnictide
superconductors, suggesting a unified scenario for the iron-based
superconductors. Moreover, the superconducting transition is significantly
broadened upon applying a magnetic field, indicating strong thermal fluctuation
effects in the superconducting state of
TlRbFeSe. The derived thermal activation energy
for vortex motion is compatible with those of the 1111-type iron pnictides.Comment: 7 pages, 6 figure
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