Superconductivity at High Magnetic Fields
- 1 July 1963
- journal article
- research article
- Published by American Physical Society (APS) in Physical Review B
- Vol. 131 (1), 140-157
- https://doi.org/10.1103/physrev.131.140
Abstract
Using pulsed-magnetic-field techniques, we have studied the magnetic-field-induced superconducting transitions of alloys in the systems Ti-V, Ti-Nb, Ti-Ta, Ti-Mo, Zr-Nb, Hf-Nb, Hf-Ta, U-Nb, and U-Mo. For concentrated alloys the low-current-density resistive critical field is nearly independent of the amount of cold working and the relative orientations of magnetic field, current, and anisotropic defect structure. The observed values of peak up sharply (reaching 145 kG in the Ti-Nb system) in the vicinity of ∼4.5 "valence" electrons per atom, an electron concentration where peaking also typically occurs for such (approximately) defect-independent transition metal alloy parameters as superconducting transition temperature, thermodynamic critical field, and electronic specific heat coefficient. All the above evidence suggests that in these alloys is determined principally by bulk electronic parameters, rather than by the nature of extended lattice defects. This view is further supported by the observation that, for several Group V-rich, Group IV-Group V transition metal alloys, excellent quantitative agreement is achieved in adjustable-parameter-free comparisons of with , the "upper critical field" predicted on the basis of bulk electronic parameters by the Ginzburg-Landau-Abrikosov-Gor'kov (GLAG) theory for the case of negative surface energy. For certain ranges of alloy composition, it appears that normal-state paramagnetic free-energy considerations, ignored in the GLAG theory, impose limitations on in good accord with the theoretical predictions of Clogston. Additional experimental results are reviewed, and it is argued that a comprehensive theoretical understanding of high-field superconductivity in bulk materials may be achieved on the basis of the GLAG theory, modified to include paramagnetic free-energy terms, and extended to consider transport supercurrents stabilized in a manner similar to that suggested by Gorter and Anderson. The a priori assumptions of Mendelssohn's filamentary-mesh model appear, on the other hand, to be inadequate for a suitable description.
Keywords
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