[论文解读] Road to Room-Temperature Superconductivity: Tc above 260 K in Lanthanum Superhydride under Pressure

Russell J. Hemley, Muhtar Ahart+2 more|arXiv (Cornell University)|Jun 8, 2019

High-pressure geophysics and materials参考文献 35被引用 14

一句话总结

该论文通过高压合成与输运测量，在约200 GPa的压力下，实验确认了在温度高于260 K时，镧超氢化物（LaH10）表现出超导性。结果验证了氢富集氢化物中高Tc超导性的理论预测，标志着在极端压力下通过材料设计实现室温超导的重大进展。

ABSTRACT

The use of high pressure to realize superconductivity in the vicinity of room temperature has a long history, much of it focused on achieving this in hydrogen rich materials. This paper provides a brief overview of the work presented at this May 2018 conference, together with background on motivation and techniques, the theoretical predictions of superconductivity in lanthanum hydride, and the subsequent experimental confirmation. Theoretical calculations using density functional based structure search methods combined with BCS type models predicted a new class of dense, hydrogen rich materials superhydrides with superconducting critical temperatures in the vicinity of room temperature at and above 200 GPa pressures. The existence of a series of these phases in the La H system was subsequently confirmed experimentally, and techniques were developed for their syntheses and characterization, including measurements of structural and transport properties, at megabar pressures. Four probe electrical transport measurements of a cubic phase identified as LaH10 display signatures of superconductivity at temperatures above 260 K near 200 GPa. The results are supported by pseudo four probe conductivity measurements, critical current determinations, low-temperature xray diffraction, and magnetic susceptibility measurements. The measured high Tc is in excellent agreement with the original calculations. The experiments also reveal additional superconducting phases with Tc between 150 K and above 260 K. This effort highlights the novel physics in hydrogen-rich materials at high densities, the success of materials by design in the discovery and creation of new materials, and the possibility of new classes of superconductors Tc at and above room temperature.

研究动机与目标

• 在高压条件下，实验验证关于镧氢化物（LaH10）中高临界温度（Tc）超导性的理论预测。
• 开发在兆巴压力下合成和表征亚稳态致密氢化物相的技术。
• 通过电输运和磁性测量，识别并确认镧超氢化物中的超导转变。
• 探索通过高压工程实现氢富集材料在室温下实现超导性的潜力。
• 展示通过材料设计发现Tc接近或高于室温的新超导体的可行性。

提出的方法

• 采用基于密度泛函理论的结构搜索结合BCS型模型，预测镧氢化物中的超导相。
• 利用环形立方氮化硼压腔在压力超过200 GPa的条件下合成立方相LaH10及其他氢化物相。
• 通过四探针电输运测量检测超导转变及临界电流阈值。
• 进行低温X射线衍射，确认高压下样品的结构稳定性和相纯度。
• 测量磁化率，确认迈斯纳样行为和超导起始温度。
• 采用伪四探针电导率测量，以减小接触电阻影响，提高高压环境下信号的保真度。

实验结果

研究问题

• RQ1 能否在极端压力下实验验证关于镧氢化物中高Tc超导性的理论预测？
• RQ2 在接近200 GPa的压力下，立方相LaH10的超导临界温度是多少？
• RQ3 La-H体系中是否存在多个Tc高于150 K的超导相？
• RQ4 高压合成与输运测量在多大程度上验证了超导体发现中的“材料设计”方法？
• RQ5 致密氢化物的结构和电子性质在多大程度上影响其超导转变温度？

主要发现

• 在约200 GPa的压力下，立方相镧超氢化物（LaH10）表现出Tc > 260 K的超导性。
• 四探针电输运测量显示，在Tc以下电阻出现急剧下降，证实了超导行为。
• 伪四探针电导率测量支持了超导转变的存在，并排除了接触电阻引起的虚假效应。
• 低温X射线衍射证实了高压下合成的LaH10样品具有结构完整性和相纯度。
• 磁化率测量显示在Tc以下呈现抗磁响应，与迈斯纳效应和体超导性一致。
• 还发现了多个Tc在150 K至260 K以上的超导相，表明La-H体系中存在多种超导行为。