Evl. Demello, A MODEL FOR HIGH-TEMPERATURE SUPERCONDUCTORS USING THE EXTENDED HUBBARD HAMILTONIAN, Physica. C, Superconductivity, 259(1-2), 1996, pp. 109-114
We derive a method to study the phase diagram for high-temperature sup
erconductors (HTCS's). Our starting point is the Hubbard hamiltonian w
ith a weak attractive interaction to obtain the formation of bound pai
rs. We consider this attractive potential at different positions for d
ifferent compounds. We then construct a wave function of the BCS type
by a variational method using the Fourier transform of this extended H
ubbard potential and then derive an energy gap equation which can be a
pplied to the s wave and d wave channel. This simple approach allows u
s to obtain the critical temperature as a function of the doping conce
ntration which gives very good agreement with the experimental phase d
iagrams of YBaCuO and La(Sr,Ba)CuO compounds.