La₃Ni₂O₇中交织的自旋-电荷条纹序与极性晶格畸变
Intertwined spin-charge stripe order and polar lattice distortion in La$_{3}$Ni$_{2}$O$_{7}$
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中文总结 AI 辅助
本研究通过第一性原理计算明确La₃Ni₂O₇低压态中自旋、电荷与晶格的紧密交织关系，发现其高压下自旋涨落可能介导超导配对，且最低能a-条纹态可弛豫至极性Am2m结构。
中文摘要 AI 辅助
La₃Ni₂O₇的低温密度波态具有显著的自旋密度波（SDW）序，而近期实验进一步揭示了电荷重新分布以及伴随的晶格对称性降低。然而，自旋、电荷与晶格之间的微观关系仍不明确。我们采用第一性原理计算，研究了La₃Ni₂O₇的电子结构和静态自旋 susceptibility随压力的演化，同时分析了代表性磁构型的能量学与晶格响应。我们将SDW不稳定性追溯至强费米面嵌套，发现高压下的自旋响应与T_C密切相关，这表明存在自旋涨落介导的配对。在考虑的候选磁态中，自旋-电荷-条纹态在能量上更受青睐且动态稳定，表现出显著的局域Ni磁矩和Ni-O键长的歧化。值得注意的是，能量最低的a-条纹态会通过沿b轴的极性畸变自发弛豫至实验提出的极性Am2m结构。这些结果建立了一个统一图像：在低压密度波态中，自旋、电荷与晶格响应紧密交织，而自旋涨落仍是高压下超导的合理组成部分。
英文摘要
The low-temperature density-wave state of La$_3$Ni$_2$O$_7$ hosts pronounced spin-density-wave (SDW) order, while recent experiments further reveal charge redistribution and a concomitant lattice-symmetry lowering. However, the microscopic relationship among spin, charge, and lattice remains unclear. Using first-principles calculations, we investigate the pressure evolution of the electronic structure and static spin susceptibility of La$_3$Ni$_2$O$_7$, together with the energetics and lattice response of representative magnetic configurations. We trace the SDW instability to strong Fermi-surface nesting and find that the high-pressure spin response closely tracks $T_{\mathrm C}$, suggesting spin-fluctuation-mediated pairing. Among the candidate magnetic states considered, the spin-charge-stripe states emerge as energetically favored and dynamically stable, developing pronounced disproportionation of both the local Ni moments and the Ni--O bond lengths. Remarkably, the lowest-energy a-stripe state spontaneously relaxes into the experimentally proposed polar Am2m structure through a polar distortion along the b axis. These results establish a unified picture in which spin, charge, and lattice responses are strongly intertwined in the low-pressure density-wave state, while spin fluctuations remain a plausible ingredient of superconductivity under pressure.
