AI 中文总结
本研究通过从头算方法研究最佳掺杂无限层镍酸盐的超导性质，证明其超导由自旋涨落相互作用驱动，具有符号反转的$d_{x^2-y^2}$波能隙，计算结果与多数实验一致，预测性质可立即验证。
AI 中文摘要
无限层镍酸盐最近成为一类潜在的非常规高临界温度（$T_c$）超导体新家族。然而，其超导（SC）配对机制、能隙对称性等基本问题仍存在激烈争议。本文基于超导体密度泛函理论计算，对等处理电子-声子耦合（EPC）、屏蔽库仑排斥和自旋涨落（SF）相互作用，对最佳掺杂镍酸盐$Re$$_{0.8}$Sr$_{0.2}$NiO$_2$（$Re=$ La、Pr、Nd）的超导性质开展了完全从头算的理论研究。我们发现$Re_{0.8}$Sr$_{0.2}$NiO$_2$是双带超导体，在不同费米面（FS）口袋上具有符号反转的$d_{x^2-y^2}(\text{±})$波能隙函数。有趣的是，当关闭SF相互作用时，$T_c$变得极小（~0.01 K），由此证明$Re_{0.8}$Sr$_{0.2}$NiO$_2$中的超导性由SF相互作用驱动。此外，我们的从头算计算显示，尽管EPC在布里渊区（BZ）角落的小三维电子费米口袋中占主导，但在布里渊区中心附近的大准二维费米口袋上，SF相互作用比EPC和库仑排斥都强一个数量级，因此形成了SF介导的配对机制。有节点的$d_{x^2-y^2}(\text{±})$波能隙结构的出现，可归因于布里渊区角落处林哈德响应函数的显著峰值。我们计算得到的费米面、超导临界温度、有节点能隙结构和超导准粒子态密度与现有大多数实验一致。此外，预测的非常规超导性质，如La$_{0.8}$Sr$_{0.2}$NiO$_2$和Pr$_{0.8}$Sr$_{0.2}$NiO$_2$的扫描隧道谱，可立即开展实验验证。
英文摘要
Infinite-layer nickelates have recently emerged as a new family of potential unconventional high critical temperature ($T_c$) superconductors. However, fundamental questions such as their superconducting (SC) pairing mechanism and gap symmetry remain under intense debate. Here we present a fully {\it ab initio} theoretical study on the SC properties of optimally doped nickelates $Re$$_{0.8}$Sr$_{0.2}$NiO$_2$ ($Re=$ La, Pr, Nd), based on the density functional theory for superconductors calculations with electron-phonon coupling (EPC), screened Coulomb repulsion and spin fluctuation (SF) interaction treated on an equal footing. We find that $Re_{0.8}$Sr$_{0.2}$NiO$_2$ are two-band superconductors with sign reversal $d_{x^2-y^2}(\pm)$-wave gap functions on the different Fermi surface (FS) pockets. Interestingly, when the SF interaction is turned off, $T_c$ becomes negligibly small ($\sim$0.01 K), thus demonstrating that the superconductivity in $Re_{0.8}$Sr$_{0.2}$NiO$_2$ is driven by SF interaction. Moreover, our {\it ab initio} calculations reveal that the SF interaction is an order of magnitude stronger than both EPC and Coulomb repulsion on the large quasi-two-dimensional FS pocket around the Brillouin zone (BZ) center, thus leading to the SF-mediated pairing mechanism, although the EPC dominates on the small three-dimensional electron FS pockets at the BZ corners. The emergence of nodal $d_{x^2-y^2}(\pm)$-wave gap structure is traced to the pronounced peaks in the Lindhard response function at the BZ corners. Our calculated FS, SC critical temperature, nodal gap structure and SC quasiparticle density of states are consistent with most available experiments. Furthermore, predicted unconventional SC properties such as scanning tunneling spectra of La$_{0.8}$Sr$_{0.2}$NiO$_2$ and Pr$_{0.8}$Sr$_{0.2}$NiO$_2$ are ready for immediate experimental verifications.
Comments13 pages, 11 figures and 3 tables
