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Helfand, Eugene; Werthamer, N. R.

doi:10.1103/physrevlett.13.686

Cited by 267 publications

(156 citation statements)

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“…Although fuller characterization of paramagnetic limitation and spin-orbit scattering effects, as well as strong coupling corrections and nonspherical Fermi surfaces, is provided by Werthamer and co-workers, [48][49][50][51][52] we did not find that this added any additional insight into our data on inhomogeneous Nb 3 Sn conductors.…”

Section: B Data Reduction Techniquesmentioning

confidence: 44%

“…The inhomogeneities that are present in practical wires, combined with the lack of accurate A15 resistivity data, however, rule out rigorous connections to microscopic theories. For theoretical connections to the fundamental parameters, as well as for corrections of the applied approximations, physically more exact descriptions have been developed [48][49][50][51][52] and applied. 1,17,53,54 These more exact descriptions all result, however, in an increased number of fitting parameters, the details of which are impossible to obtain for real, inhomogeneous wire samples.…”

Section: The Use Of the Mdg Descriptionmentioning

confidence: 99%

“…Moreover, the zero-temperature Kramer 14 -extrapolated critical field ͓ 0 H K ͑0͔͒ often results in values far beyond 30 T. 10 This seems unrealistically high in comparison to actual measured results, which are limited to about 29.5 T for higher resistivity, slightly Sn-poor pure Nb-Sn film. 2 Expressions for the H-T phase transition, derived directly from the BCS theory, are readily available in the literature, [44][45][46][47][48][49][50][51][52] and have been applied with success to welldefined laboratory specimens, 1,17,53,54 but most of the H-T data on wires are empirically described. 36,37,41 This leads to continuing discussions in the literature, partly resulting from the use of extrapolated values of 0 H c2 ͑0͒ without taking into account the inhomogeneous nature of the conductors.…”

Section: Introductionmentioning

confidence: 99%

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The upper critical field of filamentary Nb3Sn conductors

Godeke

Jewell

Fischer

et al. 2005

Journal of Applied Physics

104

128

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We have examined the upper critical field of a large and representative set of present multifilamentary Nb 3 Sn wires and one bulk sample over a temperature range from 1.4 K up to the zero-field critical temperature. Since all present wires use a solid-state diffusion reaction to form the A15 layers, inhomogeneities with respect to Sn content are inevitable, in contrast to some previously studied homogeneous samples. Our study emphasizes the effects that these inevitable inhomogeneities have on the field-temperature phase boundary. The property inhomogeneities are extracted from field-dependent resistive transitions which we find broaden with increasing inhomogeneity. The upper 90%-99% of the transitions clearly separates alloyed and binary wires but a pure, Cu-free binary bulk sample also exhibits a zero-temperature critical field that is comparable to the ternary wires. The highest 0 H c2 detected in the ternary wires are remarkably constant: The highest zero-temperature upper critical fields and zero-field critical temperatures fall within 29.5± 0.3 and 17.8± 0.3 K, respectively, independent of the wire layout. The complete field-temperature phase boundary can be described very well with the relatively simple Maki-DeGennes model using a two-parameter fit, independent of composition, strain state, sample layout, or applied critical state criterion.

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Section: B Data Reduction Techniquesmentioning

confidence: 44%

Section: The Use Of the Mdg Descriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

The upper critical field of filamentary Nb3Sn conductors

Godeke

Jewell

Fischer

et al. 2005

Journal of Applied Physics

104

128

View full text Add to dashboard Cite

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“…A linear dependence of B c2|| down to 0.1 T c has been revealed within our previous investigations of Ge:Ga [5]. The theory of Werthamer, Helfand, and Hohenberg describes B c2 (T) for superconductors in the dirty limit, i.e., where the Ginzburg-Landau coherence length is restricted by short electronic mean-free paths [28][29][30]. This condition is fulfilled for heavily Ga-doped Ge.…”

Section: Superconducting Propertiesmentioning

confidence: 88%

The impact of heavy Ga doping on superconductivity in germanium

Skrotzki

Herrmannsdörfer

Heera

et al. 2011

Low Temperature Physics

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We report new experimental results on how superconductivity in gallium-doped germanium (Ge:Ga) is influenced by hole concentration and microstructure. Ion implantation and subsequent flash-lamp annealing at various temperatures have been utilized to prepare highly p-doped thin films consisting of nanocrystalline and epitaxially grown sublayers with Ga-peak concentrations of up to 8 at.%. Successive structural investigations were carried out by means of Rutherford-backscattering spectrometry in combination with ion channelling, secondaryion-mass spectrometry, and high-resolution cross-sectional transmission electron microscopy. Hole densities of 1.8·10 20 to 5.3·10 20 cm -3 (0.4 to 1.2 at.%) were estimated via Hall-effect measurements revealing that only a fraction of the incorporated gallium has been activated electrically to generate free charge carriers. The coincidence of a sufficiently high hole and Ga concentration is required for the formation of a superconducting condensate. Our data reflect a critical hole concentration of around 0.4 at.%. Higher concentrations lead to an increase of T c from 0.24 to 0.43 K as characterized by electrical-transport measurements. A short mean-free path indicates superconductivity in the dirty limit. In addition, small critical-current densities of max. 20 kA/m 2 point to a large impact of the microstructure.PACS: 74.10.+v Occurrence, potential candidates; 74.78.-w Superconducting films and low-dimensional structures.

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“…A. Abrikosov, L. P. Gor'kov and P. W. Anderson. The upper critical field theory of the type II superconductors was systematically studied by N. R. Werthamer, at coworkers [70,71,72,73,74]. For the conventional superconductors, BCS theory works very well, however it was unable to interpret many properties in the high T c superconductors assuming electron-phonon interaction as the pairing mechanism.…”

Section: Chapter 2 Overview Of Superconductivitymentioning

confidence: 99%

Structural/magnetic phase transitions and superconductivity in Ba(Fe1-xTMx)2As2 (TM=Co, Ni, Cu, Co/Cu, Rh and Pd) single crystals

2009

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Temperature and Purity Dependence of the Superconducting Critical Field,Hc2

Cited by 267 publications

References 1 publication

The upper critical field of filamentary Nb3Sn conductors

The upper critical field of filamentary Nb3Sn conductors

The impact of heavy Ga doping on superconductivity in germanium

Structural/magnetic phase transitions and superconductivity in Ba(Fe<sub>1-x</sub>TM<sub>x</sub>)<sub>2</sub>As<sub>2</sub> (TM=Co, Ni, Cu, Co/Cu, Rh and Pd) single crystals

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