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Physics Letters A

Singlet pairing in the single-band Hubbard model: contributions of second order in t/U

V. Yu. Yushankhaï, G. M. Vujičić, R. B. Žakula

Published Dec 1, 1990• 19 citations
Publisher
DOI
10.1016/0375-9601(90)90766-h

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The mean field Green function solution of the two-band singlet-hole Hubbard model for high-T c superconductivity in cuprates (N.M. Plakida et al., Phys. Rev. B51, 16599 (1995), JETP 97, 331 (2003)) involves expressions of higher order correlation functions describing respectively the singlet hopping and the superconducting pairing. Rigorous derivation of their values is reported based on the finding that specific invariant classes of polynomial Green functions in terms of the Wannier overlap coefficients v ij exist.
The one-dimensional Hubbard model with first- and second-neighbor hopping, t1 and t2, with t2≊t1/(2)1/2 and large repulsion U, is proposed as a testing ground of Anderson’s idea that the existence of an resonating valence bond ground state in the half-filled-band case will show superconductivity when a finite concentration of holes is introduced. Interestingly, our preliminary calculations in the U=∞ limit for small chains have revealed a new mechanism for enhancement of singlet pairing: We find that for t2<0 the ground state is a singlet, and, for t2<0 and ‖t2/t1‖≪1, the nearest-neighbor extended-singlet-pairing correlation function becomes enhanced appreciably as the temperature decreases below t2.