标题： 在吸引 Hubbard 模型中通过分层增加超导$T_c$ 显示英文标题

标题： Increasing superconducting $T_c$ by layering in the attractive Hubbard model

摘要： 吸引Hubbard模型已成为在光晶格上用超冷原子容易实现的模型。 然而，超导（超流）临界温度，$T_c$，仍然比实验中达到的最低温度稍低。 在这里，我们考虑两种可能的途径，统称为分层，以增加$T_c$：一种是双层结构，另一种是具有可调跃迁的简单立方晶格，$t_z$，在吸引Hubbard平面之间。 我们进行了无负号的行列式量子蒙特卡洛模拟，计算了响应函数，如配对关联函数、均匀自旋磁化率和双重占据，通过这些我们描绘了一些物理性质。 我们发现，通过合理选择填充度和局域吸引力的强度，双层结构可以表现出1.5到1.7倍于单层的$T_c$；对于简单立方晶格，增强效果可以比单层的最大值高出30%。 我们还验证了在吸引Hubbard模型中对$T_c$的类似BCS的估计的准确性，以及基于超流密度的$T_c$上限的准确性。 显示英文摘要

摘要： The attractive Hubbard model has become a model readily realizable with ultracold atoms on optical lattices. However, the superconducting (superfluid) critical temperatures, $T_c$'s, are still somewhat smaller than the lowest temperatures achieved in experiments. Here we consider two possible routes, generically called layering, to increase $T_c$: a bilayer and a simple cubic lattice, both with tunable hopping, $t_z$, between attractive Hubbard planes. We have performed minus-sign--free determinant quantum Monte Carlo simulations to calculate response functions such as pairing correlation functions, uniform spin susceptibility, and double occupancy, through which we map out some physical properties. We have found that by a judicious choice of fillings and intensity of on-site attraction, a bilayer can exhibit $T_c$'s between 1.5 and 1.7 times those of the single layer; for the simple-cubic lattice the enhancement can be 30\% larger than the maximum for the single layer. We also check the accuracy of both a BCS-like estimate for $T_c$ in the attractive Hubbard model, as well as of an upper bound for $T_c$ based on the superfluid density.