Spin-free quantum chemistry. XXVI. The Ising, small-bipolaron theory of cuprate superconductivity
✍ Scribed by F. A. Matsen
- Publisher
- John Wiley and Sons
- Year
- 1996
- Tongue
- English
- Weight
- 598 KB
- Volume
- 57
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
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, JBH, between them. The energy gap, A(O>, 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 meanfield theory to the highly degenerate ground-state yields a second-order phase change with kT,/2 = JBH and a real order parameter, R(T), which is valid over the entire temperature range from zero to T, . Near T, , 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. 0 1996 John Wiley & Sons, Inc.