共查询到20条相似文献,搜索用时 15 毫秒
1.
I. F. Voloshin A. V. Kalinov L. M. Fisher S. A. Derevyanko V. A. Yampol’skii 《JETP Letters》2001,73(6):285-288
Experimental and theoretical studies of the magnetization curves M(H) obtained for plates of an anisotropic hard superconductor are performed. The samples are YBCO single-domain textured crystals with the c axis lying in the sample plane. It is shown that, for some orientations of the magnetic field in the sample plane, the magnetization curves contain additional extrema; at the same time, the virgin magnetization curve M(H) exhibits features characteristic of the peak effect. This proves that the anisotropy of the current-carrying ability can give rise to a new type of peak effect. 相似文献
2.
In an isotropic type II superconductor in a moderate magnetic field, the transition to the normal state occurs by vortex lattice melting. In certain anisotropic cases, the vortices acquire elongated cross sections and interactions. Systems of anisotropic, interacting constituents generally exhibit liquid crystalline phases. We examine the possibility of a two step melting in homogeneous type II superconductors with anisotropic superfluid stiffness from a vortex lattice into first a vortex smectic and then a vortex nematic at high temperature and magnetic field. We find that fluctuations of the ordered phase favor an instability to an intermediate smectic-A in the absence of intrinsic pinning. 相似文献
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A. L. Rakhmanov L. M. Fisher A. A. Levchenko V. A. Yampol’skii M. Baziljevich T. H. Johansen 《JETP Letters》2002,76(5):291-294
The instability of a magnetic flux flow in a system of vortices and antivortices in superconductors with a power (exponent m) anisotropic current-voltage characteristic was studied theoretically. It was shown that instability arose even at a comparatively weak anisotropy of the current-carrying properties of a superconductor if m?1. The dispersion equation determining the dependence of the increment of instability growth on the wave number was derived and analyzed. 相似文献
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A theory of μSR method is developed for uniaxial anisotropic high-T
c superconductors. In two extreme cases ofH
ext‖c
andH
ext⊥c
analytical formulas are obtained which makes it possible to determine from the position of van Hove singularities in the
Fourier-spectrum of muonium polarization, the type and parameters of the vortex lattice, such as λ
ab
(λ
c
). In caseH
ext≲H
c2 we obtained the shape of the Fourier-spectrum in analytical form and the simple method of determining the Ginsburg-Landau
parameter κ.
Convenient expressions for numerical calculations are obtained for the arbitrary orientation of the external field, and an
algorithm is provided to compute the mean fieldB, the vortex lattice parameters and the bulk field distribution in anisotropic superconductor. The Fourier spectrum of polarization
based on these calculations can be used to independently check the validity of the high-T
c parameters determination for “appropriate” orientations. 相似文献
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The theories governing the magnetic behavior of Type II superconductors assume reversible magnetization curves. However, due to imperfections and inhomogeneities, many superconductors possess hysteretic curves. A theory is proposed which allows a ‘reversible’ curve to be found from the two irreversible curves. The ‘reversible’ curve is an approximation to the exact Abrikosov reversible curve for Hc1 ≤ H ≤ Hc2. The theory agrees closely with experimental results. 相似文献
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The Bi2Sr2CaCu2O8 system is viewed as an archetypal of superconductors modelled as Josephson coupled CuO2 bilayers. The isothermal and temperature dependent DC and AC magnetization measurements forH‖c in a single crystal of Bi2212 have been performed. Qualitative changes are observed to occur over a narrow range of temperature
values before reaching the superconducting-normal transition. The observed behaviour can be ascribed to the rapid variation
in the strength of the coupling between the superconducting CuO2 planes (i.e., bilayers in the case of Bi2212). Strongly coupled planes behave like a 3D superconductor, whereas weakly coupled
planes have a two component response attributable to 2D planes and interplanar couplings. We believe that this paper is a
plethora of new findings. Our observations imply that resistivity across the planes becomes zero earlier than that within
the planes. A new line (designated asH
2D(T)) above which the change in the electromagnetic response is dominated by quasi 2D-planes has been determined for the first
time. This paper also contains the first observation of Differential Diamagnetic Effect (DDE) in the In-phase AC susceptibility
data which signals the onset (atT
2D(H)) of dominance of response from 2D-planes. In addition to a host of interesting thermomagnetic history effects which are
a consequence of interplay between the diamagnetic responses from the two components, a comparison of irreversibility lines
(of the 3D state) determined by different methods on the same specimen of a HTSC is also being presented for the first time.
We have come across Paramagnetic Meissner Effect (PME), first recognized in ceramic samples of Bi2212, in the temperature
region of dimensional crossover in our single crystal sample, whichinter-alia confirms our labelling of the two component behaviour. A schematic phase diagram summarizing the various transformations
that can occur nearT
c in the electromagnetic response of an anisotropic layered system has been drawn. 相似文献
12.
M. Ciszek G. Kozlowski P. Tekiel E.A. Gijsbertse L.J.M. van de Klundert 《Physics letters. A》1980,77(4):271-273
Theoretical predictions with respect to a minimum in the ac losses in type II superconductors are compared with experimental results on Nb-50% Ti and Nb-10% Mo. Extensions of the theory are suggested to explain the deviations. 相似文献
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The combined effect of a surface (edge) barrier and volume pinning on the dependence of critical current I c on the magnetic field (I⊥H 0) in bulk type II superconductors is investigated. In low magnetic fields, there is a portion of the curve I c(H 0) where I c grows with H 0, causing a nontrivial peak effect in this field range. Such behavior is explained by the combined effect of a surface (edge) barrier and volume pinning, the latter being rather sensitive to the transport current density distribution in a superconductor. 相似文献
15.
W. E. Timms 《Physics letters. A》1972,40(5):427-428
It seems possible that, under certain field and current conditions, the critical current of a type II superconductor is not determined simply by application of a Bean-London model, but by the joint use of the latter and a second equation. 相似文献
16.
Dr. M. H. Khan 《Zeitschrift für Physik B Condensed Matter》1968,8(3):209-215
Using the two fluid model, modified Londons equations have been obtained for the type II superconductors in the Schubnikov state (H c1<H<H c2). The effect of the normal electrons which form the cores of the flux vortices have been included. These equations can be reduced to the Londons equations under suitable assumptions. The electric field inside the superconductor and the field equations have also been obtained. 相似文献
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Measurement of the flux flow noise have been made in foil samples of Pb80In20. The results obtained cannot be explained by previous models which assume direct transit of fluxoids across sample. However, using a model based on the assumption that the flux motion is interrupted by pinning centers it is possible to obtain a good fit to the measured noise curves. Good agreement is also obtained between the calculated and measured critical frequencies using this model. These results may also help explain certain features of noise measurements reported by other workers. 相似文献
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