[论文解读] Superconductivity in infinite-layer lanthanide nickelates

Shengwei Zeng, Changjian Li+9 more|arXiv (Cornell University)|May 27, 2021

Iron-based superconductors research参考文献 27被引用 25

一句话总结

本研究报道了钙掺杂的无限层LaNiO2薄膜中存在超导性，其在0.15 < x < 0.3范围内呈现超导穹形相图，而在未掺杂和轻掺杂区域则表现出绝缘行为。与钕和镨基镍氧化物不同，霍尔系数符号变化发生在所有掺杂水平下约35 K的温度，表明其多带结构受晶格关联影响，具有独特性。

ABSTRACT

The origin of high-Tc superconductivity remains an enigma even though tremendous research effort and progress have been made on cuprate and iron pnictide superconductors. Aiming to mimic the cuprate-like electronic configuration of transition metal, superconductivity has been recently found in nickelates. This discovery hallmarks a new era in the search and understanding of the high-Tc superconductivity. However, unlike the cuprate and iron pnictide, in which the superconductivity was initially found in a compound containing La, the superconductivity in the nickelate has only been observed in Nd- and Pr-based compounds. This raises a central question of whether the f electron of the rare-earth element is critical for superconductivity in the nickelates. Here, we report the observation of superconductivity in infinite-layer Ca-doped LaNiO2 (La1-xCaxNiO2) thin films and construct their phase diagram. Unlike the metal-insulator transition in Nd- and Pr-based nickelates, the undoped and underdoped La1-xCaxNiO2 thin films are entirely insulating from 300 down to 2 K. A superconducting dome is observed from 0.15<x<0.3 with weakly insulating behavior at the overdoped regime. Moreover, the sign of the Hall coefficient RH changes at low temperature for samples with a higher doping level. However, distinct from the Nd- and Pr-based nickelates, the RH-sign-change temperature remains around 35 K as the doping increases, suggesting a different multiband structure in the La1-xCaxNiO2. These results also emphasize the significant role of lattice correlation on the multiband structures of the infinite-layer nickelates.

研究动机与目标

• 研究在钕和镨基体系之外的无限层稀土镍氧化物中，超导性的出现机制。
• 确定稀土元素中的f电子是否对镍氧化物中的超导性至关重要。
• 构建钙掺杂LaNiO2薄膜的相图，并理解其电子相变行为。
• 考察晶格关联在塑造这些材料多带电子结构中的作用。

提出的方法

• 通过脉冲激光沉积法外延生长La1-xCaxNiO2薄膜，以实现精确的掺杂控制。
• 从300 K降至2 K进行输运测量，包括电阻率和霍尔系数，以探测电子行为。
• 通过分析不同钙掺杂水平（x）下温度依赖的电阻率和霍尔系数数据，构建相图。
• 跟踪霍尔系数符号变化随掺杂浓度和温度的变化，以推断载流子类型和多带贡献。
• 与钕和镨基镍氧化物进行对比分析，评估f电子构型的作用。

实验结果

研究问题

• RQ1 当稀土阳离子为镧而非钕或镨时，无限层镍氧化物中的超导性是否仍然存在？
• RQ2 稀土阳离子中f电子的存在是否对镍氧化物中的超导性至关重要？
• RQ3 与钕和镨基体系相比，La1-xCaxNiO2中的多带电子结构如何演化？
• RQ4 晶格关联在塑造无限层镍氧化物电子性质方面发挥何种作用？
• RQ5 为何在La1-xCaxNiO2中，霍尔系数符号变化发生在所有掺杂水平下恒定的温度（约35 K）？

主要发现

• 在钙掺杂的LaNiO2薄膜中观测到超导性，其超导穹形相图位于0.15 < x < 0.3范围内。
• 未掺杂和轻掺杂的La1-xCaxNiO2薄膜从300 K至2 K始终保持绝缘态，与钕和镨基镍氧化物中观察到的金属-绝缘体转变形成鲜明对比。
• 所有较高掺杂水平下，霍尔系数符号变化均发生在约35 K，表明存在稳定的多带结构。
• 霍尔系数行为表明，La1-xCaxNiO2的电子结构与钕和镨基镍氧化物存在差异，尽管掺杂水平相似。
• 晶格关联被确定为影响无限层镍氧化物中多带电子结构的关键因素。