NANOSCOPIC PHASE SEPARATION AND THE UNIVERSAL TRANSPORT AND MAGNETIC PROPERTIES OF HIGH Tc SUPERCONDUCTORS

1999 ◽  
Vol 13 (29n31) ◽  
pp. 3528-3531
Author(s):  
J. JUNG ◽  
H. YAN ◽  
H. DARHMAOUI ◽  
M. ABDELHADI
Keyword(s):  
Magnetic Properties ◽  
Phase Separation ◽  
Temperature Dependence ◽  
Current Density ◽  
Low Temperatures ◽  
Energy Barrier ◽  
Vortex Motion ◽  
Superfluid Density ◽  
High Tc Superconductors ◽  
High Tc

We have found the correlation between nanoscopic phase separation in the copper-oxygen planes of YBCO and TlBCCO and the transport and magnetic properties of these materials in the a-b planes such as: the temperature dependence of the critical current density Jc( T ), the temperature dependence of the superfluid density ns( T )∝1/λ2( T ) at low temperatures, the temperature dependence of the normalized logarithmic relaxation rate S(T), and the dependence of the effective energy barrier against vortex motion on the current density Ueff( J ). These properties are controlled by the ratio of the amount of an underdoped filamentary phase to that of an optimally doped one.

MICROWAVE ABSORPTION STUDIES ON HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS VII — ESR OF DPPH COATED ON A THIN BiSrCaCuO FILM FABRICATED ON MgO(100) SUBSTRATE

1992 ◽  
Vol 06 (11) ◽  
pp. 675-682
Author(s):  
K. SUGAWARA ◽  
T. SUGIMOTO ◽  
Y. SHIOHARA ◽  
S. TANAKA
Keyword(s):  
Magnetic Field ◽  
Critical Current Density ◽  
Temperature Dependence ◽  
Microwave Absorption ◽  
Current Density ◽  
Applied Magnetic Field ◽  
High Tc Superconductors ◽  
High Tc ◽  
Absorption Studies ◽  
Mpmg Method

ESR of DPPH coated on a Bi-Sr-Ca-Cu-O (BSCCO) film (350 Å thick) fabricated on MgO(100) substrate by MOCVD was studied. Temperature dependence of the ESR peak-to-peak linewidth, ΔH pp , and the effect of applied magnetic field on ΔH pp have been studied below about 100 K. The results were compared with those of ESR of DPPH coated on ceramic Y-Ba-Cu-O samples (powder and bulk) made by the MPMG method. The DPPH ESR for the BSCCO film revealed that ΔH pp was independent of applied magnetic field up to about 9 kG. In addition, no similarity between the temperature dependence of the excess ESR linewidth of the DPPH and that of critical current density was found for the BSCCO film. These results for the BSCCO film are different from those for the MPMG YBCO samples.

THE SURFACE IMPEDANCE OF HIGH Tc SUPERCONDUCTORS

1989 ◽  
Vol 03 (01) ◽  
pp. 5-13 ◽  
Author(s):  
J. CARINI ◽  
L. DRABECK ◽  
G. GRÜNER
Keyword(s):  
High Temperature ◽  
Temperature Dependence ◽  
Power Law ◽  
Surface Impedance ◽  
Low Temperatures ◽  
Qualitative Agreement ◽  
Surface Resistance ◽  
High Temperature Superconductors ◽  
High Tc Superconductors ◽  
High Tc

Recent experiments on the surface impedance of the high temperature superconductors are summarized. The overall temperature dependence of the penetration depth is in broad qualitative agreement with conventional pairing, but with an anomolous power law behavior observed at low temperatures. The surface resistance is orders of magnitude larger than estimates based on the Mattis-Bardeen theory. One possibility is unconventional pairing, but structural inhomogenities are the most likely explanation for the experimental results.

Direct Determination of the Velocity of Vortices in High-Tc Superconductors by a Non-Equilibrium Method

1998 ◽  
Vol 12 (29n31) ◽  
pp. 3288-3291
Author(s):  
I. Kirschner ◽  
R. Laiho ◽  
A. C. Bódi ◽  
E. Lähderanta ◽  
I. Vajda
Keyword(s):  
Magnetic Field ◽  
Temperature Gradient ◽  
Vortex Motion ◽  
Direct Determination ◽  
Field Investigation ◽  
High Tc Superconductors ◽  
High Tc ◽  
Pinning Centers ◽  
Non Equilibrium

As is shown, thermally assisted vortex motion can come into being in high-T c superconductors due to the applied temperature gradient. Its behavior strongly depends on the local and global microstructure of the samples, moreover on the temperature and magnetic field. Investigation of the density, size and intensity of the pinning centers of specimens leads to the conclusion that the higher homogeneity immediately weakens and the lower one strenghtens the pinning, thus the former promotes and the latter impedes the vortex motion. The non-equilibrium experimental technique together with a.c. susceptibility measurements render possible the direct determination of the velocity of vortices. Depending on the actual microstructural state of samples it has the values between 6 × 10-2 mm/s and 18 × 10-2 mm/s in the case of Y-Ba-Cu-O specimens investigated.

MAGNETIC PROPERTIES OF THE HIGH Tc SUPERCONDUCTORS BiSrCaCuO AND TlBaCaCuO

1989 ◽  
Vol 03 (01) ◽  
pp. 77-85 ◽  
Author(s):  
Y. D. DAI ◽  
C. LIN ◽  
W. B. ZHANG ◽  
S. Q. FENG ◽  
X. ZHU ◽  
...  
Keyword(s):  
Magnetic Properties ◽  
Flux Pinning ◽  
Magnetic Hysteresis ◽  
Hysteresis Loops ◽  
High Tc Superconductors ◽  
Magnetic Current ◽  
High Tc ◽  
Bean Model ◽  
Current Densities ◽  
Magnetic Hysteresis Loops

Magnetic properties of the high T c superconductors BiSrCaCuO and TlBaCaCuO were investigated systematically. Magnetic current densities were calculated from magnetic hysteresis loops of bulk and powdered samples by Bean model. The results showed that flux pinning in these materials is much weaker than that in YBaCuO.

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