Three-site interactions and superconductivity of itinerant spins: A high-temperature expansion

C. Bastide; C. Lacroix

doi:10.1103/PhysRevB.43.6232

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Three-site interactions and superconductivity of itinerant spins: A high-temperature expansion

C. Bastide, C. Lacroix

DOI 10.1103/PhysRevB.43.6232 · Physical Review B

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Abstract

We consider hard-core fermions on a single-band lattice additionally with nearest-neighbor two-site and three-site two-body interactions. We derive exact high-temperature expansions of the superconducting susceptibilities and correlation functions for different pair symmetries. These results can serve as a useful test of approximate theories. As an example, a mean-field treatment of the nearest-neighbor interactions is found to underestimate the susceptibility enhancement. In addition, the three-site interaction appears in the exact expansion to be as important as the two-site interaction, even in the case of nearly localized spins.