三层 La$_4$Ni$_3$O$_{10}$ 在压力下的电子结构与磁性倾向：结构转变、分子轨道与层间分化
Electronic structure and magnetic tendencies of trilayer La$_4$Ni$_3$O$_{10}$ under pressure: structural transition, molecular orbitals, and layer differentiation
AI总结：
该研究通过第一性原理计算揭示三层镍酸盐 La$_4$Ni$_3$O$_{10}$ 在压力下发生结构相变并伴随超导电性，其电子结构由分子三聚体轨道描述，磁性基态为内层非磁、外层条纹反铁磁的独特堆叠，且 $d_{x^2-y^2}$ 轨道在低能物理中起关键作用。
摘要：
受近期在加压三层 La$_4$Ni$_3$O$_{10}$ Ruddlesden-Popper (RP) 镍酸盐中观察到超导电性的启发，我们通过第一性原理计算研究了其结构、电子和磁性性质随静水压力的变化。我们发现，在双层和三层镍酸盐中，正交（单斜）到四方的结构转变在压力下与超导电性的出现同时发生。La$_4$Ni$_3$O$_{10}$ 的电子结构可以通过分子三聚体基组来理解，其中 $n$ 个分子子带源于 $d_{z^2}$ 轨道在层内沿 $c$ 轴的强杂化。磁性倾向表明，环境压力下的基态由非磁性的内层和条纹有序的外层构成，这些外层沿 $c$ 轴反铁磁耦合，从而形成一种不寻常的 $\uparrow$, 0, $\downarrow$ 堆叠，这与中子衍射所提出的自旋密度波模型一致。这种状态在超导电性出现的压力下失稳。尽管费米能级处存在 $d_{z^2}$ 态，$d_{x^2-y^2}$ 轨道在 La$_4$Ni$_3$O$_{10}$ 的电子结构中也起着关键作用。$d_{x^2-y^2}$ 态在低能物理中的这种积极作用，以及内层和外层不同的电子行为，与多层铜氧化物超导体的物理相似。
英文摘要：
Motivated by the recent observation of superconductivity in the pressurized trilayer La$_4$Ni$_3$O$_{10}$ Ruddlesden-Popper (RP) nickelate, we explore its structural, electronic, and magnetic properties as a function of hydrostatic pressure from first-principles calculations. We find that in both the bilayer and trilayer nickelates, an orthorhombic(monoclinic)-to-tetragonal transition under pressure takes place concomitantly with the onset of superconductivity. The electronic structure of La$_4$Ni$_3$O$_{10}$ can be understood using a molecular trimer basis wherein $n$ molecular subbands arise as the $d_{z^2}$ orbitals hybridize strongly along the $c$-axis within the trilayer. The magnetic tendencies indicate that the ground state at ambient pressure is formed by nonmagnetic inner planes and stripe-ordered outer planes that are antiferromagnetically coupled along the $c$ axis, resulting in an unusual $\uparrow$, 0, $\downarrow$ stacking that is consistent with the spin density wave model suggested by neutron diffraction. Such a state is destabilized by the pressures wherein superconductivity arises. Despite the presence of $d_{z^2}$ states at the Fermi level, the $d_{x^2-y^2}$ orbitals also play a key role in the electronic structure of La$_4$Ni$_3$O$_{10}$. This active role of the $d_{x^2-y^2}$ states in the low-energy physics of the trilayer RP nickelate, together with the distinct electronic behavior of inner and outer planes, resembles the physics of multilayer cuprates.
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