Fluctuations of vortices in Josephson-coupled superconductors

Bulaevskiǐ, L. N.; Maley, M. P.; Cho, J.H.

doi:10.1016/0921-4534(94)91321-8

Cited by 5 publications

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“…The thermal fluctuation of the vortex lines gives an entropy contribution to the free energy and thus to the magnetization M = ∂F/∂H a . Bulaevskii et al (1992cBulaevskii et al ( , 1994c predicted that all magnetization curves M (H a , T ) should cross in one point if M is plotted versus the temperature T with the applied field H a as a parameter. At this crossing point one has…”

Section: Vortex Fluctuations Modify the Magnetizationmentioning

confidence: 99%

The flux-line lattice in superconductors

1995

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Magnetic flux can penetrate a type-II superconductor in form of Abrikosov vortices (also called flux lines, flux tubes, or fluxons) each carrying a quantum of magnetic flux φ 0 = h/2e. These tiny vortices of supercurrent tend to arrange in a triangular flux-line lattice (FLL) which is more or less perturbed by material inhomogeneities that pin the flux lines, and in high-T c superconductors (HTSC's) also by thermal fluctuations. Many properties of the FLL are well described by the phenomenological Ginzburg-Landau theory or by the electromagnetic London theory, which treats the vortex core as a singularity. In Nb alloys and HTSC's the FLL is very soft mainly because of the large magnetic penetration depth λ: The shear modulus of the FLL is c 66 ∼ 1/λ 2 , and the tilt modulus c 44 (k) ∼ (1 + k 2 λ 2 ) −1 is dispersive and becomes very small for short distortion wavelength 2π/k ≪ λ. This softness is enhanced further by the pronounced anisotropy and layered structure of HTSC's, which strongly increases the penetration depth for currents along the c-axis of these (nearly uniaxial) crystals and may even cause a decoupling of two-dimensional vortex lattices in the Cu-O layers. Thermal fluctuations and softening may "melt" the FLL and cause thermally activated depinning of the flux lines or of the two-dimensional "pancake vortices" in the layers. Various phase transitions are predicted for the FLL in layered HTSC's. Although large pinning forces and high critical currents have been achieved, the small depinning energy so far prevents the application of HTSC's as conductors at high temperatures except in cases when the applied current and the surrounding magnetic field are small.

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Section: Vortex Fluctuations Modify the Magnetizationmentioning

confidence: 99%