Usefulness of the Hubbard-I approximation for study of superconducting properties of the repulsive Hubbard model with large U is investigated. Electron pair correlation function for the Hubbard model is calculated with the help of generalized Hubbard-I approximation. We compare d-wave part of such correlation function with the equal-time d-wave propagator found in quantum Monte Carlo simulation. The both functions decay as a/r3 when separation r between the pair insertion and pair extraction points is large (coefficient a is independent of r). However, the Hubbard-I approximation underestimates coefficient a by a factor of the order of 2. Our work demonstrates that Hubbard-I approximation may be used as a simple yet reliable tool for investigating superconducting properties of the Hubbard model.
- Hubbard model
- Hubbard-I approximation