Third-order perturbation analysis for p- and d-wave pairing states in two-dimensional repulsive Hubbard model Original Research Article

We study instability of a singlet and triplet pairing states in a quasi-two-dimensional Hubbard model on the basis of the third-order perturbation theory. Comparing the result obtained here with that is obtained by using only the second-order effective interaction, a stable p-wave state spreads from low to intermediate density region. The vertex correction of the third-order effective interaction makes a dx2−y2-wave state for the high density near half-filling. On the other hand, the third-order term makes the p-wave state dominant.