Theory of the critical current in two-band superconductors with application to MgB2
E. J. Nicol, J. P. Carbotte
DOI 10.1103/PhysRevB.72.014520 · Physical Review B
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Abstract
Using a Green’s function formulation of the superfluid current js, where a momentum qs is applied to the Cooper pair, we have calculated js as a function of qs, temperature, and impurity scattering for a two-band superconductor. We consider both renormalized BCS and full strong-coupling Eliashberg theory. There are two peaks in the current as a function of qs due to the two energy scales for the gaps, and this can give rise to nonstandard behavior for the critical current. The critical current jc, which is given as the maximum in js, can exhibit a kink as a function of temperature as the maximum is transferred from one peak to other. Other temperature variations are also possible and the universal BCS behavior is violated. The details depend on the material parameters of the system, such as the amount of coupling between the bands, the gap anisotropy, the Fermi velocities, and the density of states of each band. The Ginzburg-Landau relation between jc, the penetration depth λL, and thermodynamic critical field Hc is modified. Using Eliashberg theory with the electron-phonon spectral densities given from band structure calculations, we have applied our calculations for js and jc to the case of MgB2 and find agreement with experiment.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| MgB2 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 39 | Pressure not reported | unknown |
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