Enhancement of the d_{x^2-y^2} pairing correlation in the two-dimensional Hubbard model: a quantum Monte Carlo study

Abstract

Quantum Monte Carlo is used to investigate the possibility of d_{x^2-y^2} superconductivity in the two-dimensional repulsive Hubbard model. A small energy scale relevant to possible pairing requires a care (i.e., sufficiently small level separation between the $k$ points $(δk,π-δk')$ and $(π-δk'',δk''')$ with small $δk$'s) to detect enhanced correlations in finite-size studies, as motivated from a previous study on Hubbard ladders. Our calculation indeed detects long-tailed enhancements in the d_{x^2-y^2} pairing correlation when the system is near, but not exactly at, half-filling.