Nonadiabatic theory of the superconducting state
M. Botti, E. Cappelluti, C. Grimaldi, L. Pietronero
DOI 10.1103/PhysRevB.66.054532 · Physical Review B
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Abstract
The nonadiabatic theory of superconductivity has provided a useful tool to investigate the superconducting properties of narrow-band systems where Fermi energy EF is comparable with the phonon frequencies ωph. Here we present the extention of nonadiabatic theory to the superconducting state (T<Tc) and we derive the generalized Eliashberg equations that include the first nonadiabatic diagrams arising from the breakdown of Migdal’s theorem. We show that the opening of the superconducting gap modifies the momentum-frequency structure of the electron-phonon vertex function with respect to normal state. We study the effects of nonadiabatic terms on the superconducting gap Δ and on the ratio 2Δ/Tc in order to relate possible strong-coupling phenomenology, signalized by 2Δ/Tc>3.53, and nonadiabatic effects.
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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