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  • Access by Xinjiang University

Magnetic Properties of Type-II Superconductors in the Two-Band Model

C. C. Sung*

  • Department of Physics, Ohio State University, Columbus, Ohio 43210

  • *Research sponsored in part by the Air Force Office of Scientific Research, U. S. Air Force, under Grant No. AF-AFOSR-68-1487, through the Ohio State University Research Foundation.

Phys. Rev. 187, 548 – Published 10 November, 1969

DOI: https://doi.org/10.1103/PhysRev.187.548

Abstract

It has been suggested previously by Wong and Sung that the present discrepancies between theory and experiments on the magnetic properties of some transition metals which are intrinsic type-II superconductors (e.g., Nb) may be caused by the overlapping-band effect of s and d bands. We present here the numerical results of this effect on the magnetic properties. It is shown that the overlapping-band effect in the pure limit can reduce the upper critical field Hc2 about 30-60% at T close to temperature Tc, and thus enhance the over-all temperature dependence of Hc2. The amount of reduction decreases as the superconductors become dirtier. Reasonable parameters which characterize the overlapping-band effect are assumed. We also compute κ2, which defines the slope of Hc2 when the external field is slightly less than Hc2. It is found that κ2 becomes smaller in comparison with the present theory as TTc; thus a stronger temperature dependence is also associated with κ2. The numerical value of this correction in κ2, however, is very sensitive to the parameters used.

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