Orientational Dependence of the Flux-Flow Resistivity and Critical Current Density in Type-II Superconducting Foils

1968 ◽  
Vol 168 (2) ◽  
pp. 413-417 ◽  
Author(s):  
W. C. H. Joiner ◽  
G. E. Kuhl
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Type Ii ◽  
Flux Flow ◽  
Flow Resistivity

Critical Currents in NbSe2: Evidence for Surface Pinning

1972 ◽  
Vol 50 (22) ◽  
pp. 2840-2841 ◽  
Author(s):  
J. Kopp ◽  
D. J. Huntley ◽  
R. F. Frindt
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Critical Currents ◽  
Flux Flow ◽  
Flux Lines

The variation of critical current density for flux flow with thickness has been measured for crystals of NbSe2 between 10−6 and 0.03 cm thick. The dominant behavior is that [Formula: see text] (thickness)−1 and this is interpreted as evidence for surface pinning predominating over bulk pinning of the flux lines.

Properties and Defects of Type II Superconductors

MRS Bulletin ◽  
1991 ◽  
Vol 16 (12) ◽  
pp. 37-41 ◽  
Author(s):  
Donglu Shi
Keyword(s):  
Crystal Structure ◽  
Transition Temperature ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Type Ii ◽  
Critical Transition ◽  
Critical Transition Temperature ◽  
High Degree ◽  
Superconducting Parameters

Three major superconducting parameters can characterize a type II superconductor: critical transition temperature, Tc, upper critical magnetic field, Hc2, and critical current density, Jc. Because of the variety of crystal structures, chemical stoichiometrics, and microstructures of the materials, these superconducting parameters differ greatly from system to system.It has been found that the critical transition temperature is closely related to the crystal structure and stoichiometry. Previous studies have shown that compounds with a high degree of symmetry tend to be more favorable to superconductivity. Compounds with a cubic structure, such as a bcc structure, usually have higher Tc values than compounds with a hexagonal lattice. Among conventional superconductors, the so-called A-15 structure is most favorable for high transition temperatures. It is well known that many high Tc superconductors such as YBa2Cu3Ox and Bi2Sr2CaCu2Ox have an orthorhombic structure with a high degree of symmetry.The upper critical field, Hc2, is more complicated in terms of its relationship to structural characteristics. Experimental results have indicated that Hc2 is more closely related to the chemical stoichiometry and crystal structure than to the microstructure.However, the critical current density, Jc, can vary tremendously in a compound with a given crystal structure. The change in critical current density is associated with the so-called flux pinning that arises from the interaction between the flux lines and crystal defects. Thus, Jc is determined mostly by the microstructure of the materials.

EFFECTS OF QUANTUM AND THERMAL FLUCTUATIONS ON COLLECTIVE PINNING AND CRITICAL CURRENT DENSITY IN TYPE-II SUPERCONDUCTING BULK MATERIALS

2011 ◽  
Vol 25 (04) ◽  
pp. 609-618
Author(s):  
MING JU CHOU ◽  
HERNG ER HORNG
Keyword(s):  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Thermal Fluctuations ◽  
Quantum Limit ◽  
Type Ii ◽  
Type Ii Superconductors ◽  
Collective Pinning ◽  
Fluctuation Temperature ◽  
Increasing Temperature

The effects of quantum and thermal fluctuations on collective pinning and critical current density Jc are investigated for bulk type-II superconductors by utilizing quantum statistics. It is shown that for a constant magnetic field, Jc is nearly independent of temperature in the quantum limit; however, in the classical limit, Jc decreases weakly with increasing temperature when T < Tdp (depinning temperature); when Tdp < T < Tf (boundary fluctuation temperature), Jc is power-law-decaying, and when T > Tf, Jc decays exponentially. For constant temperature, Jc first decreases, then increases after reaching a maximum, and finally decreases again. These results are in agreement with the experiments.

Electron diffraction contrast of fluxons

1991 ◽  
Vol 49 ◽  
pp. 1102-1103
Author(s):  
L.C. Qin ◽  
L.D. Marks
Keyword(s):  
Magnetic Field ◽  
Electron Diffraction ◽  
Critical Current Density ◽  
Critical Current ◽  
Current Density ◽  
Scanning Tunneling ◽  
Type Ii ◽  
Tunneling Microscopy ◽  
Type Ii Superconductors ◽  
Diffraction Contrast

Partial penetration of an applied external magnetic field occurs in type-II superconductors. The properties of magnetic fluxons are important in determining the critical current density of type-II superconductors as it is the mobility of the fluxon lattice that limits the high value of critical current density of superconductors. There have been various experimental techniques in use to study the fluxons, e.g. the decoration technique, neutron diffraction, electron holography and scanning tunneling microscopy.Noting that in the thin crystal case the magnetic fluxes have a tangential component which deflects incident electrons, we explore the possibility of using conventional electron diffraction contrast technique to observe the fluxons. This is accomplished by using the London model for the vortex in thin crystals and the classical electromagnetic theory based on Maxwell equations to construct the magnetic field of a fluxon.

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