超导La$_{3}$Ni$_{2}$O$_{7}$中d$_{xy}$与s$_{\pm }$配对对称性的竞争源于LDA+FLEX计算
Competing d$_{xy}$ and s$_{\pm }$ Pairing Symmetries in Superconducting La$_{3}$Ni$_{2}$O$_{7}$ emerge from LDA+FLEX Calculations
AI总结：
本研究通过LDA+FLEX计算揭示超导La$_{3}$Ni$_{2}$O$_{7}$中d$_{xy}$与s$_{\pm }$配对对称性的竞争，为理解镍基超导机制提供关键预测。
摘要：
随着无限层镍酸盐以及高压下La$_{3}$Ni$_{2}$O$_{7}$中超导性的最新发现，出现了新的机遇，即自然界中可能存在另一类基于Ni元素的高温超导体，正如先前铜氧化物和铁基材料的情况。由于3d电子间著名的强库仑关联以及接近反铁磁不稳定性，这些系统对理论描述构成了挑战，且大多数先前的超导研究依赖于简化少轨道模型哈密顿量的求解。另一方面，在此我们使用最近开发的密度泛函理论与从所谓的涨落交换（FLEX）型随机相位近似（RPA）推导出的动量及频率分辨自能的组合，来研究压力下La$_{3}$Ni$_{2}$O$_{7}$中自旋涨落介导的配对倾向。该方法使用实际材料的第一性原理电子结构，且不依赖于模型哈密顿量方法中采用的紧束缚参数化。基于我们对BCS能隙方程的数值对角化，我们表明在超导La$_{3}$Ni$_{2}$O$_{7}$中出现了竞争的d$_{xy}$和s$_{\pm }$配对对称性，相应的耦合常数在自旋密度波不稳定性附近变得很大。本文呈现的结果在众多其他计算的背景下进行了讨论，并为正在进行的实验工作提供了预测，这些预测将允许进一步检验我们对非常规超导体的理解。
英文摘要：
With recent discoveries of superconductivity in infinite--layer nickelates, and in La$_{3}$Ni$_{2}$O$_{7}$ under high pressure, new opportunities appeared that yet another family of high--temperature superconductors based on Ni element may exist in Nature as was previously the case of cuprates and iron based materials. With their famous strong Coulomb correlations among 3d electrons and the proximity to antiferromagnetic instability these systems represent a challenge for their theoretical description, and most previous studies of superconductivity relied on the solutions of simplified few--orbital model Hamiltonians. Here, on the other hand, we use a recently developed combination of density functional theory with momentum and frequency resolved self--energies deduced from the so--called Fluctuational--Exchange (FLEX)--type Random Phase Approximation (RPA) to study spin fluctuation mediated pairing tendencies in La$_{3}$Ni$_{2}$O$_{7}$ under pressure. This methodology uses first--principle electronic structures of an actual material and is free of tight--binding parametrizations employed in model Hamiltonian approach. Based on our numerical diagonalization of the BCS Gap equation we show that competing d$_{xy}$ and s$_{\pm }$ pairing symmetries emerge in superconducting La$_{3}$Ni$_{2}$O$% _{7}$ with the corresponding coupling constants becoming large in the proximity of spin density wave instability. The results presented here are discussed in light of numerous other calculations and provide on--going experimental efforts with predictions that will allow further tests of our understanding of unconventional superconductors.
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