Effect of hopping anisotropy on the d-wave pairing in the Hubbard model: From two-leg ladder to square lattice

Abstract

In the ladder-type cuprates, superconductivity is argued to be enhanced by increasing the electron hopping in the rung direction, while such an enhancement is not expected in the layered cuprates. Utilizing the quantum Monte Carlo calculations of the Hubbard model, we study the effect of the hopping anisotropy on the d-wave pairing, on the two-leg ladder, the square lattice and the coupled two-leg ladder lattice. On the square lattice, the hopping anisotropy monotonically suppresses the d-wave pairing; while on the two-leg ladder, an optimal hopping anisotropy for the d-wave pairing exists at tx/ty≈0.6. For the coupled two-leg ladder lattice, as the coupling strength ty′/ty decreases, the evolution of the d-wave pairing as a function of the hopping anisotropy behaves as a crossover from the square lattice to the two-leg ladder. Our results provide numerical proof for the possible enhancement of superconductivity in both the ladder-type and layered cuprates.