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[论文解读] High-temperature superconductivity in A15-type La4H23 below 100 GPa

Sam Y. Cross, Jonathan Buhot|arXiv (Cornell University)|Aug 6, 2023
Advanced Chemical Physics Studies被引用 4
一句话总结

本研究在95 GPa压力下实现了A15型La4H23的高温超导，临界转变温度约为90 K，通过在氨硼烷中对Pd帽化La薄膜进行激光加热实现。超导相通过XRD和电阻率测量得到证实，进一步支持氢笼结构在降低压力下氢化物中实现高Tc超导的关键作用。

ABSTRACT

High-temperature superconductivity has been observed in binary hydrides such as LaH10 at pressures above 150 GPa. Hydrogen cage structures have been identified as a common motif beneficial for high critical temperatures Tc. Efforts are now focused on finding hydride high-temperature superconductors at lower pressures. We present evidence for high-temperature superconductivity in binary La4H23 with A15-type structure featuring hydrogen cages at a pressure of P = 95 GPa. We synthesise La4H23 from a lanthanum film capped with a palladium catalyst promoting the dissociation of hydrogen. In resistance measurements, we observe superconductivity with a transition temperature Tc = 90 K. In X-ray diffraction on the same sample, we identify the A15-type cubic body centred structure of the lanthanum sublattice. From comparison with earlier XRD and structure prediction studies, we identify this phase with La4H23. Our study reinforces the concept of hydrogen cages for high-temperature superconductivity.

研究动机与目标

  • 在低于100 GPa的压力下，实验验证A15型La4H23的高温超导性。
  • 研究氢笼结构在稳定二元镧氢化物中高Tc超导性中的作用。
  • 开发一种利用Pd帽化La薄膜和氨硼烷的合成路线，以在高压下实现氢扩散和相形成。
  • 通过原位X射线衍射确认La4H23的A15型立方体心结构。
  • 在同一试样中测量超导转变温度及其在磁场下的电阻率依赖性。

提出的方法

  • 通过在金刚石对顶砧中使用氨硼烷作为氢源，对260 nm厚的Pd帽化镧薄膜进行激光加热，合成La4H23。
  • 采用波长为1064 nm的YAG激光，以300 ms脉冲形式加热，使温度达到约1000 K，促进氢扩散和反应。
  • 在Diamond Light Source的I15束线进行原位X射线衍射，使用波长为0.425 Å的射线和Pilatus3 X CdTe 2M探测器。
  • 通过Rietveld和Le Bail精修XRD图谱，识别A15型结构并排除竞争相的存在。
  • 采用10 µA激励电流的四点电阻率测量，检测超导转变及最高达12 T磁场下的抑制行为。
  • 利用金刚石对顶砧边缘的拉曼位移（基于Akahama标度）进行压力校准。
Figure 1: Detection of the A-15 structure in X-Ray diffraction. (a) Rietveld and Le Bail refinements of La 4 H 23 to the observed XRD pattern shown by the solid red and grey lines respectively. Data between $11\text{\,}\mathrm{\SIUnitSymbolDegree}13\text{\,}\mathrm{\SIUnitSymbolDegree}$ are dominate
Figure 1: Detection of the A-15 structure in X-Ray diffraction. (a) Rietveld and Le Bail refinements of La 4 H 23 to the observed XRD pattern shown by the solid red and grey lines respectively. Data between $11\text{\,}\mathrm{\SIUnitSymbolDegree}13\text{\,}\mathrm{\SIUnitSymbolDegree}$ are dominate

实验结果

研究问题

  • RQ1是否能在低于100 GPa的压力下观察到A15型La4H23的高温超导性？
  • RQ2La4H23中的A15型结构（具有氢笼）是否支持高于90 K的临界温度？
  • RQ3Pd帽化镧薄膜是否能在高压下实现La4H23的高效氢化和相形成？
  • RQ4在95 GPa下，La-H体系中该超导相的结构身份是什么？与理论预测和先前观测到的相相比如何？
  • RQ5La4H23的超导转变如何响应外加磁场？这对它的相干长度和上临界磁场有何启示？

主要发现

  • 通过四点电阻率测量，在95 GPa下观察到La4H23的超导转变，Tc ≈ 90 K。
  • X射线衍射证实La4H23具有A15型立方体心结构（空间群Pm3̄n），特征衍射峰位于2θ ≈ 7.5–10°和13.5–16°。
  • 通过Rietveld和Le Bail精修识别出A15结构，晶胞参数与La4H23一致，且不同于其他已知氢化物。
  • 从电极和样品制备中检测到残留的金属镧（Fmmm）和金（Fm3̄m），但未发现LaH4、LaH9或LaCH2等竞争相的证据。
  • 磁场研究显示，在Tc以下电阻率被抑制至12 T，证实了该转变的超导本质。
  • 初始La薄膜的剩余电阻率比（RRR）约为2.5，纯La在95 GPa下的超导转变温度为Tc = 8.6 K，略高于以往报道，可能由于压力梯度的影响。
Figure 2: Detection of superconductivity in La 4 H 23 and resistance measurements on subsequent cooling runs. In each case, cooling and warming measurements are indicated. The value of $T_{\text{c}}$ was determined at the onset of superconductivity from the intersection of linear fits to the normal
Figure 2: Detection of superconductivity in La 4 H 23 and resistance measurements on subsequent cooling runs. In each case, cooling and warming measurements are indicated. The value of $T_{\text{c}}$ was determined at the onset of superconductivity from the intersection of linear fits to the normal

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