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Garcia, A.; Xx, Zhang; Tejada, J.; Manzel, M.; Bruchlos, H.

doi:10.1103/physrevb.50.9439

Cited by 9 publications

(3 citation statements)

References 24 publications

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“…In numerous experiments the creep rate plotted versus T appears to tend to a finite value at zero temperature. Flux creep observed at low temperatures by Lensink et al (1989), Mota et al (1989Mota et al ( , 1991, Griessen et al (1990), Fruchter et al (1991, Lairson et al (1991), Liu et al (1992), Prost et al (1993), andGarcía et al (1994), and in ultrathin Nb wires by Ling et al (1995), in principle may be explained by usual thermal activation from smooth shallow pinning wells (Griessen 1991), but more likely it indicates "quantum creep" or "quantum tunnelling" of vortices out of the pins as suggested first by Glazman and Fogel' (1984a) and Mitin (1987). The thermal depinning rate ∝ exp(−U/k B T ) is now replaced by the tunnelling rate ∝ exp(−S E /h) where S E is the Euklidean action of the considered tunnelling process; see Seidler et al (1995) for a recent measurement of S E .…”

Section: Depinning By Tunnellingmentioning

confidence: 97%

“…A very general theory of collective creep and of vortex-mass dominated quantum creep in anisotropic and layered superconductors is given by and a short review on flux tunnelling by Fruchter et al (1994). Since their coherence length is so small, HTSC's may belong to a class of very clean type-II superconductors in which quantum tunnelling of vortices is governed by the Hall term (Feigel'man et al 1993b, García et al 1994. Macroscopic tunnelling of a vortex out of a SQUID (a small superconducting loop with two Josephson junctions) was calculated in the underdamped case (Ivlev and Ovchinnikov 1987) and in the overdamped limit (Morais-Smith et al 1994).…”

Section: Depinning By Tunnellingmentioning

confidence: 99%

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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: Depinning By Tunnellingmentioning

confidence: 97%

Section: Depinning By Tunnellingmentioning

confidence: 99%

The flux-line lattice in superconductors

1995

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“…CCC devices rely on persistent shielding currents, thus, the magnetic field from the CCC windings should be below that which causes the circulating current to exceed the bulk critical current at the surface in the thick film of Tl-2223. This field is of order 10 A/m at 77 K [2], while in typical Tl-2223 crystalline grains, the penetration depth is of order 0.6 m [3] and the critical field is about 12 000 A/m. Crystal grains in Tl-2223 may be in the form of overlapping flat plates, which may increase the field needed to break the Josephson coupling.…”

Section: Introductionmentioning

confidence: 91%

Cryogenic current comparator measurements at 77 K using thallium-2223 thick-film shields

Elmquist

1999

IEEE Trans. Instrum. Meas.

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Several different magnetic shield geometries were used to study cryogenic current comparator (CCC) operation with thallium-based thick film superconducting shields at 77 K. These shields are found to have good magnetic shielding properties and to support low-level persistent currents. This study investigates geometric properties of the magnetic coupling between the CCC and one type of superconducting quantum interference device (SQUID) sensor. The sensitivity of the SQUID and its coupling to the shielding currents limit ten-to-one CCC resistance ratio measurements to approximately 0.2 = in relative uncertainty.

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