Peak effect due to competing vortex ground states in superconductors with large inclusions

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

doi:10.1103/physrevb.98.054517

Cited by 17 publications

(12 citation statements)

References 60 publications

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“…[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. Such a situation is realized at small and intermediate fields with a 0 ξ and a not too large pinning energy e p .…”

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: A Strong Pinningmentioning

confidence: 99%

“…where the thermal characteristic goes over into the T = 0 excess-current characteristic. From the condition (35) and using Eq. (36), we find that the relevant depinning barrier U dp (x jp + ) can be written in the form…”

Section: A Qualitative Overviewmentioning

confidence: 99%

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

et al. 2019

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“…The J c can be increased significantly by introducing artificial pinning centers. It depends on a complex interplay of individual pinning centers, the interaction between vortices, and thermal fluctuations [5][6][7]. One of the most relevant parameters in producing highly functional superconducting materials is the current-carrying capacity.…”

Section: Introductionmentioning

confidence: 99%

Sharp peak of the critical current density in BaFe2−xNixAs2 at optimal composition

et al. 2020

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The importance of type-II superconductors with strong pinning comes from their ability to carry large electrical currents in the presence of a magnetic field. We report on the results of the bulk magnetization measurements in the superconducting state in high-quality single crystals of BaFe 2−x Ni x As 2 at various doping levels ranging from the underdoped to the overdoped regimes. The zero-temperature superconducting critical current density J c at optimal composition x = 0.10, where the superconducting transition temperature T c reaches a maximum of 19.9(0.4) K, displays a pronounced sharp peak in the doping dependence. Thus the observed doping dependence of the critical current implies that pinning becomes stronger upon initial doping. In addition, the best pinning conditions are realized in the presence of structural and magnetic domains. Our results strongly suggest that the high J c values are mainly due to collective (weak) pinning of vortices by dense microscopic point defects with some contribution from a strong pinning mechanism. The experimental results of the normalized J c present a remarkably good agreement with the δl pinning theoretical curve, confirming that pinning in our samples originates from spatial variations of the charge carrier mean free path leading to small bundle vortex pinning by randomly distributed (weak) pinning centers for H c.

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“…The critical current densities J c in type-II superconductors depend on a complex interplay of individual pinning centers, the interaction between vortices, and thermal fluctuations [1,2]. The discovery of iron-based superconductors (Fe-SCs) has allowed for an expansion of the knowledge about the influence of intrinsic superconductor parameters on the resulting vortex dynamics [3,4].…”

Section: Introductionmentioning

confidence: 99%

Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)
Haberkorn
¹
,
Xu
²
,
Meier
³

et al. 2019
Phys. Rev. B
15
4
29
0
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We study the correlation between chemical composition and vortex dynamics in Ni-doped CaK(Fe1−xNix)4As4 (x=0, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities Jc and the flux creep rates S. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent μ within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (U0<100K). The undoped crystals display modest Jc values at low temperatures and high magnetic fields applied along the c axis. Jc(T) dependences at high fields display an unusual peak. The enhancement in Jc(T) matches with an increase in U0 and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in Tc there is a nonmonotonic change in Jc. Initially Jc increases, reaching a maximum value for x=0.015, and then Jc decreases for x≥0.025. This change in Jc(x) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of Jc(H) also manifests a change in behavior between these x values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent μ with Ni content, x. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation.We study the correlation between chemical composition and vortex dynamics in Ni-doped CaK(Fe 1−x Ni x ) 4 As 4 (x = 0, 0.015, 0.025, 0.03, and 0.05) single crystals by performing measurements of the critical current densities J c and the flux creep rates S. The magnetic relaxation of all the crystals is well described by the collective creep theory. The samples display a glassy exponent μ within the predictions for vortex bundles in a weak pinning scenario and relatively small characteristic pinning energy (U 0 < 100 K). The undoped crystals display modest J c values at low temperatures and high magnetic fields applied along the c axis. J c (T ) dependences at high fields display an unusual peak. The enhancement in J c (T ) matches with an increase in U 0 and the appearance of a second peak in the magnetization. As Ni doping increases, whereas there is a monotonic decrease in T c there is a nonmonotonic change in J c . Initially J c increases, reaching a maximum value for x = 0.015, and then J c decreases for x 0.025. This change in J c (x) is coincident with the onset of antiferromagnetic order. The magnetic field dependence of J c (H ) also manifests a change in behavior between these x values. The analysis of the vortex dynamics for small and intermediate magnetic fields shows a gradual evolution in the glassy exponent μ with Ni content, x. This implies that there is no appreciable change in the mechanism that determines the vortex relaxation. EFFECT OF Ni DOPING ON VORTEX PINNING IN … PHYSICAL REVIEW B 100, 064524 (2019) FIG. 2. (a)-(e) Magnetic field dependence of the critical current densities J c a...

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Peak effect due to competing vortex ground states in superconductors with large inclusions

Cited by 17 publications

References 60 publications

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

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

Sharp peak of the critical current density in BaFe2−xNixAs2 at optimal composition

Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)
Haberkorn
¹
,
Xu
²
,
Meier
³

et al. 2019
Phys. Rev. B
15
4
29
0
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Peak effect due to competing vortex ground states in superconductors with large inclusions

Cited by 17 publications

References 60 publications

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

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

Sharp peak of the critical current density in BaFe2−xNixAs2 at optimal composition

Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)Haberkorn1, Xu2, Meier3 et al. 2019Phys. Rev. B154290View full textAdd to dashboardCite

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Effect of Ni doping on vortex pinning in CaK(Fe1−xNix)
Haberkorn
¹
,
Xu
²
,
Meier
³

et al. 2019
Phys. Rev. B
15
4
29
0
View full text Add to dashboard Cite