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Spin‐free quantum chemistry. XXVI. The Ising, small‐bipolaron theory of cuprate superconductivity
Author(s) -
Matsen F. A.
Publication year - 1996
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1996)57:6<1057::aid-qua4>3.0.co;2-s
Subject(s) - bipolaron , ising model , condensed matter physics , physics , quantum mechanics , superconductivity , hamiltonian (control theory) , ground state , gauge theory , chemistry , electron , polaron , mathematical optimization , mathematics
The Ising, small‐bipolaron ( ISB ) theory is a strong‐coupling theory of cuprate superconductivity which is based on the negative‐ U , Hubbard Hamiltonian. Its ground state is composed of (small) bipolarons and (small‐bipolaron) holes with a vibronically induced, bipolaron‐hole exchange interaction, J BH , between them. The energy gap, Δ(0), is taken to be equal to the dissociation energy of a small bipolaron and which, since it is defined spectroscopically, is not an order parameter. The application of the Ising mean‐field theory to the highly degenerate ground‐state yields a second‐order phase change with kT C /2 = J BH and a real order parameter, Ω( T ), which is valid over the entire temperature range from zero to T C . Near T C , the Ising free‐energy functional takes the same form as does the Landau. In the presence of an electromagnetic field, the Ising functional is a generalization of the Ginzburg‐Landau functional which employs a complex order parameter and which is invariant under the electromagnetic gauge transformation. The breaking of the gauge invariance yields the London theory of superconductivity. © 1996 John Wiley & Sons, Inc.