Abstract

We theoretically investigate the unconventional superconductivity in the newly discovered infinite-layer nickelates Nd_1−xSr_xNiO₂ based on a two-band model. By analyzing the transport experiments, we propose that the doped holes dominantly enter the Ni d_xy or/and d_3z2−r2 orbitals as charged carriers, and form a conducting band. Via the onsite Hund coupling, the doped holes are coupled to the Ni localized holes in the d_x2−y2 orbital band. We demonstrate that this two-band model could be further reduced to a Hund-Heisenberg model. Using the reduced model, we show the non-Fermi liquid state above the critical T_c could stem from the carriers coupled to the spin fluctuations of the localized holes. In the superconducting phase, the short-range spin fluctuations mediate the carriers into Cooper pairs and establish d_x2−y2-wave superconductivity. We further predict that the doped holes ferromagnetically coupled with the local magnetic moments remain itinerant even at very low temperature, and thus the pseudogap hardly emerges in nickelates. Our work provides a new superconductivity mechanism for strongly correlated multi-orbital systems and paves a distinct way to exploring new superconductors in transition or rare-earth metal oxides.

Graphical abstract

中文翻译：

---

无限层镍酸盐中的Hund-Heisenberg模型

摘要

我们从理论上研究了基于两波段模型的新发现的无限层镍酸盐Nd _{1− x} Sr _x NiO _2中的非常规超导性。通过分析传输实验，我们提出掺杂空穴主要进入Ni d _xy或/和d _{3 z 2- r 2}轨道作为带电载流子，并形成一个导带。通过现场洪特耦合，掺杂空穴耦合到局部的Ni中的孔d _{X 2- ÿ 2}轨道带。我们证明了该两波段模型可以进一步简化为Hund-Heisenberg模型。使用简化模型，我们显示出临界T _c以上的非费米液态可能源于与局部空穴的自旋涨落耦合的载流子。在超导相，短程自旋涨落介导的载流子进入库柏对，并建立d _{X 2- ÿ 2}波超导。我们进一步预测，即使在非常低的温度下，与局部磁矩铁磁耦合的掺杂孔仍然保持流动性，因此伪间隙几乎不会出现在镍酸盐中。我们的工作为强相关的多轨道系统提供了一种新的超导机制，并为探索过渡金属或稀土金属氧化物中的新超导体铺平了道路。

图形概要