Abstract
It is shown that the ceramic superconductor YBa2Cu3O7 as well as the superconducting intermetallic compound MgB2 possesses a narrow, partly filled “superconducting band” with Wannier functions of special symmetry in their band structures. This result corroborates previous observations about the band structures of numerous superconductors and non-superconductors showing that evidently superconductivity is always connected with such superconducting bands. These findings are interpreted in the framework of a nonadiabatic extension of the Heisenberg model. Within this new group-theoretical model of correlated systems, Cooper pairs are stabilized by a nonadiabatic mechanism of constraining forces effective in narrow superconducting bands. The formation of Cooper pairs in a superconducting band is mediated by the energetically lowest boson excitations in the considered material that carry the crystal-spin angular momentum 1⋅ℏ. These crystal-spin-1 bosons are proposed to determine whether the material is a conventional low-T c or a high-T c superconductor. This interpretation provides the electron–phonon mechanism that enters the BCS theory in conventional superconductors.
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Krüger, E. Superconducting Bands Stabilizing Superconductivity in YBa2Cu3O7 and MgB2 . J Supercond Nov Magn 23, 213–223 (2010). https://doi.org/10.1007/s10948-009-0518-1
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DOI: https://doi.org/10.1007/s10948-009-0518-1