Probing the pinning landscape in type-II superconductors via Campbell penetration depth

Willa, Roland; Geshkenbeǐn, V. B.; Blatter, G.

doi:10.1103/physrevb.93.064515

Cited by 39 publications

(69 citation statements)

References 44 publications

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“…with κC = f p (r m ), see Eq. (14), and the third derivative γ = −f p (r m )/2 > 0, γ ∼ f p /ξ 3 . As long as the higher order terms in (A1) can be neglected, the bare pinning force is antisymmetric about the inflection point, The line with slopeC passing through the inflection point defines the asymptotic vortex position x m related to r m ,…”

Section: Appendix A: Marginally Strong Pinningmentioning

confidence: 98%

“…For a point-like defect, the pinning potential extends over a distance R ∼ ξ; for a defect of size σ ∼ ξ, the energy e p is determined by the condensation energy, e p ∼ H 2 c ξ 3 , see Ref. [14] for more details. Furthermore, we consider a situation where the repulsion between vortices prevents two of them from occupying the same defect 35 , limiting the interaction between vortices and the defect to the single reference vortex µ 0 ≡ 0 closest to the origin.…”

Section: A Strong Pinningmentioning

confidence: 99%

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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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Section: Appendix A: Marginally Strong Pinningmentioning

confidence: 98%

Section: A Strong Pinningmentioning

confidence: 99%

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

et al. 2019

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“…Various pinning models involving metallic and insulating defects or δT c -pinning, have been discussed in Ref. [29]; the pinning potential depth e p and the pinning strength κ then depend in various ways on λ and ξ. It turns out that the dominant contribution to the scaling near the H c2 (T )-line appears through the pinning energy e p = e p0 (1 − t − b) βe and the Labusch parameter κ = κ 0 (1 − t − b) βκ with model-dependent exponents β e and β κ .…”

Section: Parameters From Strong Pinning Theorymentioning

confidence: 99%

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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“…The Labusch constant for strong pinning caused by different types of defects was evaluated in Ref. 40.…”

Section: Pinned Vortex Parallel To the Surfacementioning

confidence: 99%

Flux expulsion in niobium superconducting radio-frequency cavities of different purity and essential contributions to the flux sensitivity

Dhakal

Ciovati

Gurevich

2020

Phys. Rev. Accel. Beams

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Magnetic flux trapped during the cooldown of superconducting radio-frequency cavities through the transition temperature due to incomplete Meissner state is known to be a significant source of radio-frequency losses. The sensitivity of flux trapping depends on the distribution and the type of defects and impurities which pin vortices, as well as the cooldown dynamics when the cavity transitions from a normal to superconducting state. Here we present the results of measurements of the flux trapping sensitivity on 1.3 GHz elliptical cavities made from large-grain niobium with different purity for different cooldown dynamics and surface treatments. The results show that lower purity material results in a higher fraction of trapped flux. We present an overview of published data on the mean free path and frequency dependence of the trapped flux sensitivity which shows a significant scatter which highlights the complexity of the pinning phenomenon on a bulk superconductor with a large curved surface. We discuss contributions of different physical mechanisms to rf losses resulting from oscillations of flexible vortex segments driven by weak rf fields. In particular, we address the dependence of the rf losses on the mean free path in the cases of sparse strong pinning defects and collective pinning by many weak defects for different orientations of the vortex with respect to the inner cavity surface. This analysis shows that the effect of the line tension of vortices is instrumental in the physics of flux trapping and rf losses, and theoretical models taking into account different pinning strength and geometry of flexible pinned vortex segments can provide a good qualitative description of the experimental data.

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Probing the pinning landscape in type-II superconductors via Campbell penetration depth

Cited by 39 publications

References 44 publications

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

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

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

Flux expulsion in niobium superconducting radio-frequency cavities of different purity and essential contributions to the flux sensitivity

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