Upper critical field in dirty two-band superconductors: Breakdown of the anisotropic Ginzburg-Landau theory

Golubov, Alexandre Avraamovitch; Koshelev, A. E.

doi:10.1103/physrevb.68.104503

Cited by 121 publications

(121 citation statements)

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“…For the qualitative description given here, we consider identical electron bands or the dominance of one major band in a two-band superconductor, which reduces to the one-band scenario for the upper critical field 31,32 . The change in anisotropy induced by the anisotropic scattering due to columnar defects can be expressed in terms of the change of the coherence lengths for both the clean and dirty limits.…”

Section: Resultsmentioning

confidence: 99%

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation

et al. 2013

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Iron-based superconductors could be useful for electricity distribution and superconducting magnet applications because of their relatively high critical current densities and upper critical fields. SmFeAsO 0.8 F 0.15 is of particular interest as it has the highest transition temperature among these materials. Here we show that by introducing a low density of correlated nano-scale defects into this material by heavy-ion irradiation, we can increase its critical current density to up to 2 Â 10 7 A cm À 2 at 5 K-the highest ever reported for an ironbased superconductor-without reducing its critical temperature of 50 K. We also observe a notable reduction in the thermodynamic superconducting anisotropy, from 8 to 4 upon irradiation. We develop a model based on anisotropic electron scattering that predicts that the superconducting anisotropy can be tailored via correlated defects in semimetallic, fully gapped type II superconductors.

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Section: Resultsmentioning

confidence: 99%

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation

et al. 2013

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“…The solid lines show the results of the strong coupling calculations [γ λ (T ) is as in Fig. 3 and γ ξ (T ) is the theory of Golubov and Koshelev [27] using the fitting parameters determined by Rydh et al Ref. [9].…”

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confidence: 99%

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

et al. 2005

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We report measurements of the temperature dependent anisotropies (γ λ and γ ξ ) of both the London penetration depth λ and the upper critical field of MgB2. Data for γ λ = λc/λa was obtained from measurements of λa and λc on a single crystal sample using a tunnel diode oscillator technique. γ ξ = H c c2 /H ⊥c c2 was deduced from field dependent specific heat measurements on the same sample. γ λ and γ ξ have opposite temperature dependencies, but close to Tc tend to a common value (γ λ ≃ γ ξ = 1.75 ± 0.05). These results are in good agreement with theories accounting for the two gap nature of MgB2.The existence of two superconducting gaps in MgB 2 [1] leads to an unusually strong temperature dependence in the anisotropy of the upper critical field, Refs. 2,3,4,5). The maximum value of γ ξ ≃ 6 is found at the lowest temperatures where it is dominated by the anisotropy in the quasi two dimensional σ bands. At higher temperatures, γ ξ is substantially reduced due to the increasing contribution of the more isotropic π band [5]. The anisotropy of the penetration depth, γ λ = λ c /λ a , is predicted to have a markedly different temperature dependence to that of H c2 [4,6]. At zero temperature, in the clean local limit, the anisotropy in the penetration depth is determined only by the anisotropy in the Fermi velocity v F and not by the anisotropy in the gap [7]. Band structure calculations [8] show that the average v F is approximately isotropic suggesting that λ is similarly isotropic at low temperature [4]. As temperature is increased it has been predicted [4,6] that γ λ increases markedly because of the more rapid reduction of the superfluid density on the π sheets (where the gap is smaller) than on the σ sheets.There have been several experimental measurements of the temperature dependence of γ ξ . Although there were some disagreements in early measurements, the most recent data [2, 3, 9] agree well with the theoretical predictions [4,5]. Significantly less experimental data has been reported on γ λ . Measurements of the distortion of the vortex lattice by neutron scattering [10] and scanning tunneling spectroscopy [11] suggest that at low temperature the anisotropy is small, γ λ = 1.2 ± 0.1. γ λ has also been estimated from the anisotropy of H c1 (γ Hc1 = H c c1 /H ⊥c c1 ). There has been some disagreement between different studies (see Ref. 12) but recent data [12] suggest that at low T , γ Hc1 ≃ 1 and there is an upward trend in γ Hc1 near T c . However, γ Hc1 may not be simply related to γ λ in MgB 2 because of two gap effects. In this paper, we present direct measurements of the temperature dependencies of λ a and λ c in single crystal samples of MgB 2 in the Meissner state, using a sensitive radio frequency technique. Our data show that γ λ increases as T → T c , in agreement with theoretical predictions. Measurements of H c2 anisotropy in the same crystals show that the values of γ λ and γ ξ converge as T → T c .Single crystals of MgB 2 were grown using a high pressure technique described elsewhere [13]. Som...

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“…The main simplification here is that the intraband scattering rates Γ π and Γ σ are assumed to be larger than the gaps, while the interband scattering rate is assumed to be negligible due to the parity argument by Mazin et al [16] discussed in the previous section. Interestingly, the strong temperature dependence of the upper critical field anisotropy was shown to exist also in this dirty limit [39]. The physical reason for this behavior is the same as in the clean limit: an interband pairing interaction of intermediate strength and a strong anisotropy of the Fermi velocities in the σ band which results in a strong anisotropy of the diffusivities in this band.…”

Section: Upper Critical Field Anisotropymentioning

confidence: 72%

“…In Refs. [38,39] such dirty limit theories of the upper critical field for MgB 2 were presented. The main simplification here is that the intraband scattering rates Γ π and Γ σ are assumed to be larger than the gaps, while the interband scattering rate is assumed to be negligible due to the parity argument by Mazin et al [16] discussed in the previous section.…”

Section: Upper Critical Field Anisotropymentioning

confidence: 99%

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Superconductivity of Magnesium Diboride: Theoretical Aspects

Dahm

Frontiers in Superconducting Materials

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In this work we review our present understanding of superconductivity in Magnesium Diboride from the theoretical perspective as it evolves from band structure calculations. Particular emphasis is placed on two gap superconductivity. Some of its peculiar consequences are discussed, in particular upper critical field anisotropy and microwave conductivity.Comment: 27 pages, 13 figures, review article to be published in: A. V. Narlikar (Ed.), Frontiers in Superconducting Materials, Springer, Berlin, 200

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Upper critical field in dirty two-band superconductors: Breakdown of the anisotropic Ginzburg-Landau theory

Cited by 121 publications

References 40 publications

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation

Huge critical current density and tailored superconducting anisotropy in SmFeAsO0.8F0.15 by low-density columnar-defect incorporation

Temperature-Dependent Anisotropy of the Penetration Depth and Coherence Length ofMgB2

Superconductivity of Magnesium Diboride: Theoretical Aspects

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