Plaquette versus ordinary d-wave pairing in the t'-Hubbard model on a width 4 cylinder
Abstract
The Hubbard model and its extensions are important microscopic models for understanding high- Tc superconductivity in cuprates. In the model with next-nearest-neighbor hopping t' (the t'- Hubbard model), pairing is strongly influenced by t' . In particular, a recent study on a width-4 cylinder observed quasi-long-rage superconducting order, associated with a negative t' , which was taken to imply superconductivity in the two-dimensional (2D) limit. In this work we study more carefully pairing in the width-4 t'-Hubbard model. We show that in this specific system, the pairing symmetry with t'<0 is not the ordinary d-wave one would expect in the 2D limit. Instead we observe a so-called plaquette d-wave pairing. The plaquette d-wave exists only on a width-4 cylinder, and so is not representative of the 2D limit. We find that a negative t' suppresses the conventional d-wave, leading to plaquette pairing. In contrast, a different t'' coupling acting diagonally on the plaquettes suppresses plaquette pairing, leading to conventional d-wave pairing.