Superconducting anisotropy and evidence for intrinsic pinning in single crystalline<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">MgB</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Takahashi, Kenichi; Atsumi, Toshiyuki; Yamamoto, Norikazu; Xu, Mingxiang; Kitazawa, Hideaki; Ishida, Toshimasa

doi:10.1103/physrevb.66.012501

Cited by 45 publications

(30 citation statements)

References 16 publications

(25 reference statements)

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“…(32) and (33), the ratio H || c2 /H ⊥ c2 is minimum at T c and increases as T decreases. This behavior has indeed been observed on many, mostly clean, M gB 2 samples 11,12,13,14,15,16,17,18,19,20,21 . By contrast, if impurities (like Al, Mg vacancies) cause the strongest intraband scattering in the "weak" π-band, (D 2 ≪ D 1 ), then the anisotropy parameter H || c2 /H ⊥ c2 would decrease as T decreases, The temperature dependence of H || c2 /H ⊥ c2 for these limiting cases is shown in Fig.…”

Section: B Temperature Dependence Of the Anisotropy Of Hc2mentioning

confidence: 79%

“…So far all attempts to increase the critical temperature T c of M gB 2 by doping have been unsuccessful 9 . On the other hand, the significant potential of M gB 2 for applications 10 is limited by comparatively low upper critical fields H ⊥ c2 (0) ≃ 3 − 5T and H || c2 (0) ≃ 15 − 19T of hexagonal M gB 2 single crystals 11,12,13,14,15,16,17,18,19,20,21 , where the indices ⊥ and || correspond to the magnetic field H perpendicular and parallel to the ab plane, respectively. As far as H c2 is concerned, it can be increased by adding nonmagnetic impurities 22,23 , which are especially effective in the dirty limit, 2πk B T c < /τ , where τ is the elastic scattering time, is the Planck constant, and k B is the Boltzmann constant.…”

Section: Introductionmentioning

confidence: 99%

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Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

2003

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Quasiclassic Uzadel equations for two-band superconductors in the dirty limit with the account of both intraband and interband scattering by nonmagnetic impurities are derived for any anisotropic Fermi surface. From these equations the Ginzburg-Landau equations, and the critical temperature Tc are obtained. An equation for the upper critical field, which determines both the temperature dependence of Hc2(T ) and the orientational dependence of Hc2(θ) as a function of the angle θ between H and the c-axis is obtained. It is shown that the shape of the Hc2(T ) curve essentially depends on the ratio of the intraband electron diffusivities D1 and D1, and can be very different from the standard one-gap dirty limit theory. In particular, the value Hc2(0) can considerably exceed 0.7TcdHc2/dTc, which can have important consequences for applications of M gB2. A scaling relation is proposed which enables one to obtain the angular dependence of Hc2(θ) from the equation for Hc2 at H c. It is shown that, depending on the relation between D1 and D2, the ratio of the upper critical field H c2 /H ⊥ c2 for H ab and H ⊥ ab can both increase and decrease as the temperature decreases. Implications of the obtained results for M gB2 are discussed.

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Section: B Temperature Dependence Of the Anisotropy Of Hc2mentioning

confidence: 79%

Section: Introductionmentioning

confidence: 99%

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

2003

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“…where R(α) = (cos 2 α + ǫ sin decreases from ≃ 2 − 3 to ≃ 1 as T decreases [46,47,48,49,50,51,52,53,54,55,56]. This behavior was explained by the two-gap theory in the clean limit [57,58,83,84].…”

Section: Anisotropy Of Hc1 and Hc2mentioning

confidence: 98%

Limits of the upper critical field in dirty two-gap superconductors

Gurevich

2007

Physica C: Superconductivity

175

189

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An overview of the theory of the upper critical field in dirty two-gap superconductors, with a particular emphasis on MgB2 is given. We focus here on the maximum Hc2 which may be achieved by increasing intraband scattering, and on the limitations imposed by weak interband scattering and paramagnetic effects. In particular, we discuss recent experiments which have recently demonstrated ten-fold increase of Hc2 in dirty carbon-doped films as compared to single crystals, so that the Hc2(0) parallel to the ab planes may approach the BCS paramagnetic limit, Hp[T ] = 1.84Tc[K] ≃ 60 − 70T . New effects produced by weak interband scattering in the two-gap Ginzburg-Landau equations and Hc2(T ) in ultrathin MgB2 films are addressed.

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“…Similarly, MgB 2 also has a layered structure, and it is described as a two-band superconductor with two gaps of Δσ and Δπ coming from boron p x,y orbitals and boron p z orbitals, respectively. Moreover, Takahashi et al [55] reported the exhibition of intrinsic pinning in single-crystalline MgB 2 by measuring the magnetic torque, and it originates from boron planes which act as the main superconducting layers in MgB 2 . The c-axis coherence length in MgB 2 is about 5 nm and even larger in the a-b plane.…”

Section: A-axis-oriented Mgb 2 Filmsmentioning

confidence: 99%

“…There are two J c peaks associated with H||ab and H||c, respectively. The peak at θ=0° can be understood as a result of the intrinsic pinning due to the layered structure of MgB 2 [55] or/and the interface pinning. The J c peak at θ=90° is believed to be originated in the grain boundaries of the columnar structure.…”

Section: Mgb 2 Columnar Thick Filmsmentioning

confidence: 99%

A review on the understanding and fabrication advancement of MgB₂thin and thick films by HPCVD

Ranot¹,

Duong²,

Bhardwaj³

et al. 2015

Progress in Superconductivity and Cryogenics

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MgB 2 thin films with superior superconducting properties are very promising for superconducting magnets, electronic devices and coated conductor electric power applications. A clear understanding of flux pinning mechanism in MgB 2 films could be a big aid in improving the performance of MgB 2 by the enhancement of J c . The fabrication advancement and the understanding of flux pinning mechanism of MgB 2 thin and thick films fabricated by using hybrid physical-chemical vapor deposition (HPCVD) are reviewed. The distinct kind of MgB 2 films, such as single-crystal like MgB 2 thin films, MgB 2 epitaxial columnar thick films, and a-axis-oriented MgB 2 films are included for flux pinning mechanism investigation. Various attempts made by researchers to improve further the flux pinning property and J c performance by means of doping in MgB 2 thin films by using HPCVD are also summarized.Keywords: MgB2 thin and thick films, HPCVD, flux pinning mechanism * Corresponding author: email: wnkang@skku.edu A review on the understanding and fabrication advancement of MgB2 thin and thick films by HPCVD CCs showed self-field J c values of the order of 10 7 A/cm 2 at 5 K as high as already obtained in MgB 2 thin films, however, J c decreases in response to an applied magnetic field [31,32]. Therefore, a complete understanding of the flux pinning mechanism could be a big aid in improving the performance of MgB 2 by the enhancement of J c , which is most important parameter in practical applications for an operation with low noise and lower power loss. The epitaxial MgB 2 thin films with uniform orientation of grains provide an ideal condition for investigating the vortex dynamics and flux pinning properties, in contrast to MgB 2 bulk system where grains are randomly orientated. In this article, we review the progress made in the last 14 years for the fabrication, understanding of flux pinning mechanism, and for improving the performance by doping in MgB 2 epitaxial thin and thick films by using HPCVD technique.

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Superconducting anisotropy and evidence for intrinsic pinning in single crystallineMgB2

Cited by 45 publications

References 16 publications

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Limits of the upper critical field in dirty two-gap superconductors

A review on the understanding and fabrication advancement of MgB₂thin and thick films by HPCVD

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Superconducting anisotropy and evidence for intrinsic pinning in single crystallineMgB2

Cited by 45 publications

References 16 publications

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Enhancement of the upper critical field by nonmagnetic impurities in dirty two-gap superconductors

Limits of the upper critical field in dirty two-gap superconductors

A review on the understanding and fabrication advancement of MgB2thin and thick films by HPCVD

Contact Info

Product

Resources

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A review on the understanding and fabrication advancement of MgB₂thin and thick films by HPCVD