Critical temperature variation with nonstoichiometry in high-temperature superconductors

Buzea, Cristina; Yamashita, Tsutomu

doi:10.1016/s0921-4534(01)00254-4

Cited by 10 publications

(11 citation statements)

References 8 publications

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“…The large width of the resistive transitions ( B c2 (T) -B * onset (T)) at all temperatures suggests the importance of dissipation processes due to depinned vortices. It is worth noting that B * onset (T) line is almost the same in all reported measurements [6]. Obviously, for practical applications this onset field is the most important one.…”

Section: Resultssupporting

confidence: 66%

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Magnetotransport and the upper critical magnetic field in MgB2

Szabó

Samuely

Jansen

et al. 2002

Physica C: Superconductivity

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Magnetotransport measurements are presented on polycrystalline MgB2 samples. The resistive upper critical magnetic field reveals a temperature dependence with a positive curvature from Tc = 39.3 K down to about 20 K, then changes to a slightly negative curvature reaching 25 T at 1.5 K. The 25- Tesla upper critical field is much higher than what is known so far on polycrystals of MgB2 but it is in agreement with recent data obtained on epitaxial MgB2 films. The deviation of Bc2(T) from standard BCS might be due to the proposed two-gap superconductivity in this compound. The observed quadratic normal-state magnetoresistance with validity of Kohler's rule can be ascribed to classical trajectory effects in the low-field limit.Comment: 6 pages, incl. 3 figure

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Section: Resultssupporting

confidence: 66%

“…Different magnitudes of the normal state magnetoresistance have been observed [2][3][4][5]. The zero-temperature value of the upper critical magnetic field B c2 (0) has been found mostly around 15 T [6]. Recently, in epitaxial films a value of about 30 Tesla for B c2 (0) has been reported with a small anisotropy [4].…”

Section: Introductionmentioning

confidence: 99%

Magnetotransport and the upper critical magnetic field in MgB2

Szabó

Samuely

Jansen

et al. 2002

Physica C: Superconductivity

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“…There is an agreement among theorists that there are two qualitatively different systems of bands in MgB 2 : quasi-2D σ-bands, and 3D πbands, and that the former strongly couple to optical E 2g phonon at ≈ 600 cm −1 . There is also experimental [6] and theoretical [5] evidence of two different superconducting gaps in this compound.…”

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confidence: 92%

Manifestation of multiband optical properties of MgB2

Kuzmenko

Mena

Molegraaf

et al. 2002

Solid State Communications

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The optical conductivity of MgB2 has been determined on a dense polycrystalline sample in the spectral range 6 meV -4.6 eV using a combination of ellipsometric and normal incidence reflectivity measurements. σ1(ω) features a narrow Drude peak with anomalously small plasma frequency (1.4 eV) and a very broad "dome" structure, which comprises the bulk of the low-energy spectral weight. This fact can be reconciled with the results of band structure calculations by assuming that charge carriers from the 2D σ-bands and the 3D π-bands have principally different impurity scattering rates and negligible interband scattering. This also explains a surprisingly small correlation between the defect concentration and Tc, expected for a two-gap superconductor. The large 3D carrier scattering rate suggests their proximity to the localization limit.

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“…However, a rapid drop of the critical current (J c ) at high fields, which could be related to weak link behavior, can be seen in most studies. 6 Several works show that the transport properties of MgB 2 are sample dependent. Both the reported resistivity at room temperature ρ(297 K) and the residual resistivity ratio, RRR=ρ(297 K)/ρ(40 K) vary among different research groups by about an order of magnitude.…”

Section: Introductionmentioning

confidence: 99%

Influence of microstructures and crystalline defects on the superconductivity of MgB2

Serquis

Liao

Zhu

et al. 2002

Journal of Applied Physics

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This work studies the influence of microstructures and crystalline defects on the superconductivity of MgB 2 , with the objective to improve its flux pinning. A MgB 2 sample pellet that was hot isostatic pressed (HIPed) was found to have significantly increased critical current density (J c ) at high fields than its un-HIPed counterpart. The HIPed sample had a J c of 10000 A/cm 2 in 50000 Oe (5 T) at 5K. This was 20 times higher than that of the un-HIPed sample, and the same as the best J c reported by other research groups. Microstructures observed in scanning and transmission electron microscopy indicate that the HIP process eliminated porosity present in the MgB 2 pellet resulting in an improved intergrain connectivity. Such improvement in intergrain connectivity was believed to prevent the steep J c drop with magnetic field H that occurred in the un-HIPed MgB 2 pellet at H > 45000 Oe (4.5 T) and T = 5 K. The HIP process was also found to disperse the MgO that existed at the grain boundaries of the un-HIPed MgB 2 pellet and to generate more dislocations in the HIPed the pellets. These dispersed MgO particles and dislocations improved flux pinning also at H<45000 Oe. The HIPing process was also found to lower the resistivity at room temperature.74.70. Ad, 74.60.Ge, 74.62.Bf, 74.25.Fy 1

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Critical temperature variation with nonstoichiometry in high-temperature superconductors

Cited by 10 publications

References 8 publications

Magnetotransport and the upper critical magnetic field in MgB2

Magnetotransport and the upper critical magnetic field in MgB2

Manifestation of multiband optical properties of MgB2

Influence of microstructures and crystalline defects on the superconductivity of MgB2

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