[论文解读] Superconductivity near 80 Kelvin in single crystals of La3Ni2O7 under pressure

Hualei Sun, Mengwu Huo+11 more|arXiv (Cornell University)|May 16, 2023

Magnetic and transport properties of perovskites and related materials参考文献 46被引用 12

一句话总结

作者报告在 La3Ni2O7 单晶在高压下（14.0–43.5 GPa）Tc 最高约 80 K 的超导性，与正交晶系 Fmmm 相及 Ni 3d 轨道–氧 p 轨道相互作用相关。

ABSTRACT

High-transition-temperature (high-T_c) superconductivity in cuprates has been discovered for more than three decades, but the underlying mechanism remains a mystery. Cuprates are the only unconventional superconducting family that host bulk superconductivity with T_cs above the liquid nitrogen boiling temperature at 77 Kelvin. Here we report an observation of superconductivity in single crystals of La3Ni2O7 with a maximum T_c of 80 Kelvin at pressures between 14.0-43.5 gigapascals using high-pressure resistance and mutual inductive magnetic susceptibility measurements. The superconducting phase under high pressure exhibits an orthorhombic structure of Fmmm space group with the 3d_(x^2-y^2 ) and 3d_(z^2 ) orbitals of Ni cations strongly interacting with oxygen 2p orbitals. Our density functional theory calculations suggest the superconductivity emerges coincidently with the metallization of the σ-bonding bands under the Fermi level, consisting of the 3d_(z^2 ) orbitals with the apical oxygens connecting Ni-O bilayers. Thus, our discoveries not only reveal important clues for the high-T_c superconductivity in this Ruddlesden-Popper double-layered perovskite nickelates but also provide a new family of compounds to investigate the high-T_c superconductivity mechanism.

研究动机与目标

• 激发在镍酸盐中寻找类似铜氧化物的高Tc 超导性的动力。
• 研究压力下 La3Ni2O7 是否能承载体相超导性。
• 确定伴随该镍酸盐超导性的结构、电子与轨道条件。
• 探讨层状镍酸盐中高Tc 超导性机制的含义。

提出的方法

• 在 La3Ni2O7 单晶上测量高压电阻和互感磁化率。
• 在 14.0 到 43.5 GPa 的范围内确定 Tc 及其对压力的依赖。
• 在超导区确定晶体结构（正交 Fmmm）。
• 进行密度泛函理论计算，将 sigma 键合带的金属化与超导性联系起来。
• 分析 Ni 3d (x2−y2, z2) 轨道与 O 2p 轨道在 Ni–O 双层中的相互作用。

实验结果

研究问题

• RQ1 在施加压力下，La3Ni2O7 单晶是否能展现体相超导性？
• RQ2 在该材料中，伴随超导性的结构相与轨道配置是什么？
• RQ3 随着压力变化，Ni 3d–O 2p 相互作用如何演变以实现超导性？

主要发现

• 在 14.0–43.5 GPa 的压力下观测到最高 Tc 为 80 K 的超导性。
• 超导相具有正交 Fmmm 结构。
• Ni 阳离子在 3d(x2−y2) 与 3d(z2) 轨道与氧 2p 轨道之间显现出强耦合。
• DFT 计算将超导性与费米面上 sigma 键合带的金属化联系起来，该带涉及 Ni 3d(z2) 轨道和 Ni–O 双层中的顶性氧原子。