Enhanced Pairing in the "Checkerboard" Hubbard Ladder

TL;DR

This study investigates how modulated hopping parameters in a checkerboard Hubbard ladder model influence superconducting pairing, revealing optimal conditions near half filling with specific interaction strengths and hopping ratios, and demonstrating enhanced pairing compared to uniform ladders.

Contribution

It demonstrates that modulated hopping parameters, especially in a checkerboard pattern, significantly enhance pairing in a Hubbard ladder, identifying optimal doping and interaction regimes.

Findings

Maximum pairing occurs near half filling with U≈6t and t'/t≈0.6.

Modulated hopping with periods 1 or 3 also enhances pairing.

Phase stiffness analysis shows energy scales for phase ordering are comparable to pairing scales.

Abstract

We study signatures of superconductivity in a 2--leg "checkerboard" Hubbard ladder model, defined as a one--dimensional (period 2) array of square plaquettes with an intra-plaquette hopping $t$ and inter-plaquette hopping $t'$, using the density matrix renormalization group method. The highest pairing scale (characterized by the spin gap or the pair binding energy, extrapolated to the thermodynamic limit) is found for doping levels close to half filling, $U\approx 6t$ and $t'/t \approx 0.6$. Other forms of modulated hopping parameters, with periods of either 1 or 3 lattice constants, are also found to enhance pairing relative to the uniform two--leg ladder, although to a lesser degree. A calculation of the phase stiffness of the ladder reveals that in the regime with the strongest pairing, the energy scale associated with phase ordering is comparable to the pairing scale.