scholarly journals THE NATURE OF SUPERCONDUCTING FLUCTUATIONS AND NEW ASPECTS IN HIGH Tc SUPERCONDUCTORS

2020 ◽  
Author(s):  
Alessandro Lascialfari ◽  
Attilio Rigamonti
Keyword(s):  
Magnetic Field ◽  
Order Parameter ◽  
Superconducting Phase ◽  
Fundamental Parameter ◽  
Magnetization Curves ◽  
High Tc Superconductors ◽  
High Tc ◽  
Phase Fluctuations ◽  
Superconducting Fluctuations ◽  
Critical Temperature Tc

After a brief introduction to thermodynamical superconducting fluctuations, some experimental results in different systems are presented. Superconducting fluctuations were predicted and revealed in nanoparticles of conventional superconductors since late 60s. However, just in the last two decades phenomena related to an anomalous diamagnetism have been discovered in high-Tc underdoped compounds, mainly by collecting the isothermal magnetization curves above the critical temperature Tc. These experimental data can be interpreted in terms of fluctuations of the phase of the order parameter and a related theoretical model can explain the results in cuprates, pnictides and Fe-based materials. Such results, here presented together with preliminary data on a Ca-based high-Tc system, allow one to extract a fundamental parameter, the upturn magnetic field above which the diamagnetic magnetization initiates to decrease on increasing the field. Its temperature dependence distinguishes among diamagnetic effects related to superconducting phase fluctuations and to analogous effects due to chemical inhomogenities.

Modelling of Hysteresis of High-Tc Superconductors

1998 ◽  
Vol 12 (29n31) ◽  
pp. 2958-2961
Author(s):  
I. Vajda ◽  
A. Szalay ◽  
L. Mohácsi ◽  
J. Lukács ◽  
T. Porjesz
Keyword(s):  
Magnetic Field ◽  
Permanent Magnets ◽  
Physical Modelling ◽  
Computer Code ◽  
Two Dimensional ◽  
Magnetization Curves ◽  
High Tc Superconductors ◽  
High Tc ◽  
Basic Ideas ◽  
The Magnetic Field

For the numerical calculation of the magnetic field and forces between HTSC materials and permanent magnets an algorithm and a two-dimensional finite difference computer code has been developed. The superconductor has been treated with its nonlinear and anisotropic dc magnetization curve. The magnetization curves are used as input characteristics for the field calculations. The basic ideas of the physical modelling are discussed.

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.

Ac Susceptibility Studies of the High Tc Superconductors: Dissipative Effects in La2.xSrxCuO4-Y and YBa2Cu3O7-Y Systems

1989 ◽  
Vol 169 ◽  
Author(s):  
Xinsheng Ling ◽  
M. E. Filipkowski ◽  
E. K. Heller ◽  
J. I. Budnick
Keyword(s):  
Grain Boundaries ◽  
Order Parameter ◽  
Ac Susceptibility ◽  
Similar Process ◽  
Charge Carrier Density ◽  
High Tc Superconductors ◽  
High Tc ◽  
Spatial Fluctuation ◽  
Dissipative Effects ◽  
Ceramic Samples

AbstractWe have studied the variation of dissipative effects with doping in the high Tc superconductors La2-xSrxCuO4-y and YBa2Cu3O7-y by studying the lossy component of ac susceptibility as a function of temperature. We find relatively strong excess losses at low temperature in both systems, which indicate stronger flux creep at grain boundaries, in lower level doped ceramic samples produced by a similar process. This effect is more significant in the La2-xSrxCuO4-y (214) system than in the YBa2Cu3O7-y(123) system. We suggest that the microscopic mechanisms of weakening of the order parameter in the grain boundaries may be different in the two systems. In the 214 system, as the charge carrier density in the CuO2 planes is reduced, the spatial fluctuation of the order parameter in the CuO2 planes is enhanced. In the 123 system, the initial removal of O from the sample, which weakens the coupling between planes and increases the spatial fluctuation of the order parameter between CuO2 planes. The grain boundaries are degraded in both systems. The degradation in the 214 samples is more significant than in the 123 samples.

MICROWAVE ABSORPTION STUDIES ON HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS VI—NON-RESONANT MICROWAVE ABSORPTION IN ULTRA-THIN Bi-Sr-Ca-Cu-O FILMS—

1992 ◽  
Vol 06 (05) ◽  
pp. 265-272 ◽  
Author(s):  
K. SUGAWARA ◽  
T. SUGIMOTO ◽  
D.J. BAAR ◽  
Y. SHIOHARA ◽  
S. TANAKA
Keyword(s):  
Magnetic Field ◽  
Microwave Absorption ◽  
Signal Intensity ◽  
Critical Magnetic Field ◽  
High Tc Superconductors ◽  
Temperature Relation ◽  
High Tc ◽  
Absorption Studies ◽  
Increasing Temperature ◽  
Mgo Substrate

Non-resonant microwave absorption (NRMA) studies have been done for Bi-Sr-Ca-Cu-O (BSCCO) films with thicknesses of 30 Å and 15 Å fabricated on MgO substrate by MOCVD. For the latter two kinds of samples have been fabricated: BSCCO/MgO and BiOx/BSCCO/MgO . NRMA signals have been detected up to about 70–75 K for all the samples. The lower critical magnetic field H c1 * of the 30 Å film was severely increased by the application of a magnetic field of several kGauss, whereas it is almost unaffected in the case of 15 Å films. H c1 * increases but the signal intensity decreases with increasing temperature for all the 30 Å and 15 Å samples. The temperature dependence of the intensity is quite different from that of thicker films (100 Å and 350 Å), in which the intensity vs. temperature relation has a peak (or peaks) at particular temperature(s).

Anomalous dependence of the dissipation upon magnetic field angle in layered high Tc superconductors

1997 ◽  
Vol 277 (3-4) ◽  
pp. 196-202 ◽  
Author(s):  
S. Aukkaravittayapan ◽  
P.J. King ◽  
Yu.I. Latyshev ◽  
R.M. Bowley
Keyword(s):  
Magnetic Field ◽  
High Tc Superconductors ◽  
High Tc ◽  
Anomalous Dependence

Low magnetic field superconducting phase diagram of the high-Tc YBa2Cu3O9-δ

1987 ◽  
Vol 64 (4) ◽  
pp. 509-511 ◽  
Author(s):  
John E. Drumheller ◽  
Gerald V. Rubenacker ◽  
W.K. Ford ◽  
J. Anderson ◽  
M. Hong ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Phase Diagram ◽  
Superconducting Phase ◽  
High Tc ◽  
Low Magnetic Field

MICROWAVE ABSORPTION STUDIES ON HIGH-Tc SUPERCONDUCTORS AND RELATED MATERIALS I—LOW-FIELD MICROWAVE ABSORPTION IN A BiSrCaCuO THIN FILM DEPOSITED BY MOCVD

1991 ◽  
Vol 05 (09) ◽  
pp. 667-674 ◽  
Author(s):  
K. SUGAWARA ◽  
T. SUGIMOTO ◽  
K. YASUIKE ◽  
D.J. BAAR ◽  
Y. SHIOHARA ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Thin Film ◽  
Microwave Absorption ◽  
Applied Field ◽  
Film Plane ◽  
Experimental Results ◽  
High Tc Superconductors ◽  
High Tc ◽  
Low Field ◽  
Absorption Studies

Non-resonant microwave absorption as a function of temperature and magnetic field has been studied in a Bi-Sr-Ca-Cu-O film prepared by MOCVD. A maximum in the absorption as a function of temperature was observed at approximately 60 K. An average Josephson loop diameter of about 0.9~1.5 microns was inferred from the experimental results. The absorption was found to depend on the angle of the film plane relative to the applied field.

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