Strong-pinning regimes by spherical inclusions in anisotropic type-II superconductors

Willa, Roland; Koshelev, A. E.; Sadovskyy, Ivan; Glatz, Andreas

doi:10.1088/1361-6668/aa939e

Cited by 47 publications

(48 citation statements)

References 68 publications

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“…6. (a) Critical current densities (a) versus magnetic field fitted to a power law jc ∝ B −α , with the exponents α at different temperatures shown in (b). The exponent α ≈ 0.5 is in good agreement with the prediction from strong pinning theory, and its decrease at high temperatures matches recent numerical results [24]. (c) Flux-flow resistivity compared to the Bardeen-Stephen formula (solid line); values below the Bardeen-Stephen line are consistent with more detailed predictions of Larkin and Ovchinikov [25].…”

Section: B A-mogesupporting

confidence: 86%

“…Taking into account a weak κ-dependence of the transverse trapping t ⊥ ∼ κ 1/4 ξ [14] changes the field-scaling of the critical current density to j c ∝ B −α with α = 5/8 for a Lorentzianshaped pinning potential. This result has been verified and augmented by numerical simulations [24] showing that the exponent α in fact decreases for increasing defect densities or vortex core size.…”

Section: Parameters From Strong Pinning Theorysupporting

confidence: 54%

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Experimental test of strong pinning and creep in current-voltage characteristics of type-II superconductors

et al. 2019

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Pinning and creep determine the current-voltage characteristic of a type II superconductor and thereby its potential for technological applications. The recent development of strong pinning theory provides us with a tool to assess a superconductor's electric properties in a quantitative way. Motivated by the observation of typical excess-current characteristics and field-scaling of critical currents, here, we analyze current-voltage characteristics measured on 2H-NbSe2 and a-MoGe type II superconductors within the setting provided by strong pinning theory. The experimentally observed shift and rounding of the voltage-onset is consistent with the predictions of strong pinning in the presence of thermal fluctuations. We find the underlying parameters determining pinning and creep and discuss their consistency.

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Section: B A-mogesupporting

confidence: 86%

Section: Parameters From Strong Pinning Theorysupporting

confidence: 54%

Experimental test of strong pinning and creep in current-voltage characteristics of type-II superconductors

et al. 2019

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“…36 For large inclusions of fixed diameter d 3ξ, the field dependence of the critical current has shown peculiar peaks, associated with the inclusion's occupancy by multiple vortices. 37,38 Similar results are observed in regular and random pinning configurations of circular (cylindrical) defects in two-dimensional (3D) systems. 31,39 Note that a 2D system with circular defects is comparable to a 3D system with columnar rather than spherical defects, see below.…”

Section: Bulk Superconductorsupporting

confidence: 67%

Edge effect pinning in mesoscopic superconducting strips with non-uniform distribution of defects

Kimmel

Glatz

Vinokur

et al. 2019

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Transport characteristics of nano-sized superconducting strips and bridges are determined by an intricate interplay of surface and bulk pinning. In the limiting case of a very narrow bridge, the critical current is mostly defined by its surface barrier, while in the opposite case of very wide strips it is dominated by its bulk pinning properties. Here we present a detailed study of the intermediate regime, where the critical current is determined, both, by randomly placed pinning centres and by the Bean-Livingston barrier at the edge of the superconducting strip in an external magnetic field. We use the time-dependent Ginzburg-Landau equations to describe the vortex dynamics and current distribution in the critical regime. Our studies reveal that while the bulk defects arrest vortex motion away from the edges, defects in their close vicinity promote vortex penetration, thus suppressing the critical current. We determine the spatial distribution of the defects optimizing the critical current and find that it is in general non-uniform and asymmetric: the barrier at the vortex-exit edge influence the critical current much stronger than the vortex-entrance edge. Furthermore, this optimized defect distribution has a more than 30% higher critical current density than a homogeneously disorder superconducting film.

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“…Let p(x) be the occupation probability of the pinned branch; the occupation probability for the free branch then is 1 − p(x). For a vortex passing centrally through the defect, the average pinning force is given by the position and occupation average (20) with f p,f pin (x) = −de p,f pin (x)/dx denoting the pinning forces on the pinned and free branches. For |x| < x − only the pinned branch is available, while for |x| > x + the occupation is restricted to the free branch; hence, we set p(x) = 1 and p(x) = 0, respectively, in those two regions.…”

Section: B Pinning Forcementioning

confidence: 99%

“…The average pinning force along the x-direction is once more given by Eq. (20), but with the pinning forces replaced by f p,f…”

Section: B Pinning Forcementioning

confidence: 99%

Strong pinning theory of thermal vortex creep in type-II superconductors

et al. 2019

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We study thermal effects on pinning and creep in type-II superconductors where vortices interact with a low density np of strong point-like defects with pinning energy ep and extension ξ, the vortex core size. Defects are classified as strong if the interaction between a single pin and an individual vortex leads to the appearance of bistable solutions describing pinned and free vortex configurations. Extending the strong pinning theory to account for thermal fluctuations, we provide a quantitative analysis of vortex depinning and creep. We determine the thermally activated transitions between bistable states using Kramer's rate theory and find the non-equilibrium steady-state occupation of vortex states. The latter depends on the temperature T and vortex velocity v and determines the current-voltage (or force-velocity) characteristic of the superconductor at finite temperatures. We find that the T = 0 linear excess-current characteristic v ∝ (j − jc) Θ(j − jc) with its sharp transition at the critical current density jc, keeps its overall shape but is modified in three ways due to thermal creep: a downward renormalization of jc to the thermal depinning current density j dp (T ) < jc, a smooth rounding of the characteristic around j dp (T ), and the appearance of thermally assisted flux flow (TAFF) v ∝ j exp(−U0/kBT ) at small drive j jc, with the activation barrier U0 defined through the energy landscape at the intersection of free and pinned branches. This characteristic emphasizes the persistence of pinning of creep at current densities beyond critical. arXiv:1903.09083v2 [cond-mat.supr-con]

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Strong-pinning regimes by spherical inclusions in anisotropic type-II superconductors

Cited by 47 publications

References 68 publications

Experimental test of strong pinning and creep in current-voltage characteristics of type-II superconductors

Experimental test of strong pinning and creep in current-voltage characteristics of type-II superconductors

Edge effect pinning in mesoscopic superconducting strips with non-uniform distribution of defects

Strong pinning theory of thermal vortex creep in type-II superconductors

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