In this study, we examine the superconducting instability of a quasi-one-dimensional lattice in the Hubbard model based on the random-phase approximation (RPA) and the fluctuation exchange (FLEX) approximation. We find that a spin-singlet pair density wave (PDW-singlet) with a center-of-mass momentum of $2k_F$ can be stabilized when the one-dimensionality becomes prominent toward the perfect nesting of the Fermi surface. The obtained pair is a mixture of even-frequency and odd-frequency singlet ones. The dominant even-frequency component does not have nodal lines on the Fermi surface. This PDW-singlet state is more favorable as compared to RPA when self-energy correction is introduced in the FLEX approximation.
The majority of fulleride superconductors with unusually high transition-temperature to kinetic-energy ratios have a face-centred-cubic (FCC) structure. We demonstrate that, within extended Hubbard models with strong Coulomb repulsion, paired fermions in FCC lattices have qualitatively different properties than pairs in other three-dimensional cubic lattices. Our results show that strongly bound, light, and small pairs can be generated in FCC lattices across a wide range of the parameter space. We estimate that such pairs can Bose condense at high temperatures even if the lattice constant is l…
We show that optical excitation of the Mott insulating phase of the one-dimensional Hubbard model can create a state possessing two of the hallmarks of superconductivity: a nonvanishing charge stiffness and long-ranged pairing correlation. By employing the exact diagonalization method, we find that the superposition of the $η$-pairing eigenstates induced by the optical pump exhibits a nonvanishing charge stiffness and a pairing correlation that decays very slowly with system size in sharp contrast to the behavior of an ensemble of thermally excited eigenstates, which has a vanishing charge sti…
The high-temperature superconducting cuprates are governed by intertwined striped magnetic and charge orders in addition to superconductivity. Remarkably similar behavior has also been seen in numerical calculations for the Hubbard model describing the copper-oxygen layers in these materials. Finite cluster methods typically find that spin and charge stripe order dominates, while embedded quantum cluster methods, which access the thermodynamic limit, often conclude that superconductivity does. Here, we report the observation of fluctuating spin and charge stripes in an embedded cluster calcula…
Pairing Tendencies in a Two-orbital Hubbard Model in One Dimension
最近在梯形化合物BaFe $_2$ S $_3$中发现的高压超导电性为铁基超导体的准一维几何结构研究开辟了新的领域。本文利用密度矩阵重整化群方法研究了一维链中的双轨道哈伯德模型。我们的主要结果是在中间Hubbard $U$排斥和鲁棒Hund耦合$J_H/U=0.25$下存在空穴结合趋势。无论是在弱耦合还是在非常强的耦合中，结合都不会发生。在接近半填充时占主导地位的对-对关联，或与电荷和自旋关联通道具有类似强度的对-对关联，涉及自旋单线态的空穴对算符，使用最近邻位点，并为每个空穴使用不同的轨道。Hund耦合强度，存在强大的磁矩，以及它们之间的反铁磁相关性是很重要的约束力的倾向，在这里找到。
Perturbation Theory for a Repulsive Hubbard Model in Quasi-One-Dimensional Superconductors
研究了准一维排斥哈伯德模型的对对称性和相变温度。我们用三阶微扰展开法求解了Eliashberg方程，并考虑了在位排斥$U$ .我们发现，当电子数密度从半充满的，过渡到非常规超导预期。当一维性较弱时，自旋单重态是有利的。相比之下，当一维性强且电子数密度远离半填充时，自旋三重态稳定。最后，我们讨论了在$β$ -Na $_{0.33}$ V $_2$ O $_5$中由在位库仑排斥引起的非常规超导电性的可能性。
Spin-triplet superconductivity in a weak-coupling Hubbard model for the quasi-one-dimensional compound Li$_{0.9}$Mo$_6$O$_{17}$
紫青铜Li $_{0.9}$ Mo $_6$ O $_{17}$由于其准一维电子结构和由此产生的可能的Luttinger液体行为而引起人们的兴趣。在足够低的温度下，它是一种具有配对对称性的超导体，但仍有待确定。为了阐明这个问题，我们分析了一个最小的哈伯德模型，这种材料涉及四个钼轨道每个单元格附近的四分之一填充，使用渐近精确微扰重整化群方法。我们发现自旋三重态奇宇称超导是主要的不稳定性。两个准一维费米面的近似嵌套特性增强了某些二阶过程，这些过程在确定配对能隙的结构中起着至关重要的作用。值得注意的是，我们发现间隙有偶然的节点，即它有更多的符号变化比所需的点群对称。
"Spin-Disentangled" Exact Diagonalization of Repulsive Hubbard Systems: Superconducting Pair Propagation
通过一种新的精确对角化技术，我们表明，束缚对之间的排斥哈伯德集群在超导的方式传播。必须处理的矩阵的大小取决于费米子组态的数量{ \em per spin}，其数量级为希尔伯特空间总大小的平方根。我们使用由弱O-O键连接的CuO $_{4}$单元来模拟铜氧化物中的面间耦合和c轴超导电性。Cu $_{2}$ O $_{8}$和Cu $_{3}$ O $_{12}$的数值结果提示了一种新的描述束缚对传播和三维几何中超导磁通量子化的解析方案。
