发表机构
Facultad de Ciencias Exactas, Ingeniería y Agrimensura; Instituto de Física Rosario (UNR-CONICET); Department of Physics, Nagoya University; Institute of Theoretical Physics, Chinese Academy of Sciences; Max Planck Institute for Solid State Research（理学院、工程学院和测量学院; 罗萨里奥物理研究所（UNR-CONICET）; 名古屋大学物理学系; 中国科学院理论物理研究所; 马克斯·普朗克固体研究所）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本文用大-N展开研究双层镍酸盐$t$-$J_\perp$-$V$模型，发现层间交换作用引发超导与环流序竞争，形成穹顶状超导区，最佳超导靠近量子临界点。
AI 中文摘要
最近在加压和薄膜双层镍酸盐中发现了具有强层间交换耦合的高温超导电性，且其与铜氧化物超导体可能存在相似性，这使得该课题成为凝聚态物理中非常活跃的研究方向。本文中，我们研究了适用于镍酸盐的强关联单轨道（$d_{x^2-y^2}$）双层 $t$-$J_\perp$-$V$ 模型，其中 $V$ 表示库仑相互作用，并采用受控的大-$N$ 展开方法在平均场水平及其之上进行分析。聚焦于面外自旋交换相互作用（$J_\perp$），我们发现它同时触发了面外 $s$ 波超导电性和面外键序相（$z$-BOP）不稳定性。$z$-BOP 产生以虚部为主的复数 $z$ 轴跃迁，驱动面外电流并诱导面内电流，在垂直方格上自发形成打破时间反演对称性的环流态。该环流相与超导电性之间的竞争产生了穹顶状超导区域，最佳超导电性出现在 $z$-BOP 量子临界点附近。由此得到的相图包含纯环流区域、低掺杂共存相、较高掺杂下的纯超导态以及关联金属态。
英文摘要
The recent discovery of high-$T_c$ superconductivity in pressurized and thin-film bilayer nickelates, featuring a strong interlayer exchange coupling, and their potential similarities with cuprate superconductors, has made this a very active topic in condensed matter physics. In the present paper we study the strongly correlated one-orbital ($d_{x^2-y^2}$) bilayer $t$-$J_\perp$-$V$ model for nickelates, where $V$ denotes the Coulomb interactions, using a controlled large-$N$ expansion at and beyond the mean-field level. Focusing on the out-of-plane spin exchange interaction ($J_\perp$), we find that it triggers both out-of-plane $s$-wave superconductivity and an out-of-plane bond-order phase ($z$-BOP) instability. The $z$-BOP gives rise to a complex $z$-axis hopping dominated by its imaginary component, which drives out-of-plane currents and induces in-plane ones, spontaneously forming on the vertical plaquettes a loop-current state that breaks time-reversal symmetry. Competition between this loop-current phase and superconductivity yields a dome-shaped superconducting region, with optimal superconductivity occurring near the $z$-BOP quantum critical point. The resulting phase diagram features a pure loop-current region, a low-doping coexistence phase, a pure superconducting state at higher doping, and a correlated metallic state.
