The attractive Hubbard model plays a paradigmatic role in the study of superconductivity (superfluidity) and has become directly realizable in ultracold atom experiments on optical lattices. However, the critical temperatures, $T_c$'s, remain lower than the lowest temperatures currently achievable in experiments. Here, we explore a possible route to enhance $T_c$ by introducing an additional next-nearest neighbor (NNN) hopping, $t^{\prime }$, in a two-dimensional square lattice. We perform sign problem-free determinant quantum Monte Carlo simulations to compute response functions such as pairing correlation functions, superfluid density, and uniform spin susceptibility. Our results show that a judicious choice of $t^{\prime }$ can increase $T_c$ by up to $50\%$ compared to the case with only nearest neighbor hopping. In contrast, the preformed pairs' temperature scale, named pairing temperature, $T_p$, decreases with increasing $|t^{\prime }/t|$, which should represent a reduction of the pseudogap region, favoring a more BCS-like behavior at intermediate coupling. We further analyze the interacting density of states to characterize the transition from a pseudogap regime to a fully gapped superconducting state. These findings suggest that NNN hopping could be a viable route to increase $T_c$ to values closer to experimentally accessible temperature scales.

Close

PrevNext

View figure in article

• Cold gases in optical lattices
• Superconductivity
• Superfluidity
• Hubbard model
• Quantum Monte Carlo