[论文解读] Conventional superconductivity at 190 K at high pressures

А. П. Дроздов, M. I. Eremets+1 more|arXiv (Cornell University)|Dec 1, 2014

High-pressure geophysics and materials参考文献 30被引用 67

一句话总结

本研究在高压（超过150 GPa）条件下报告了硫氢化物（H2S）在创纪录的190 K临界温度下出现常规超导性，其机理由强电子-声子耦合及高频声子驱动。超导性通过电阻率下降、外加磁场对Tc的抑制以及氘代D2S中显著的同位素位移得到证实，表明声子介导配对与BCS理论一致。

ABSTRACT

The highest critical temperature of superconductivity Tc has been achieved in cuprates: 133 K at ambient pressure and 164 K at high pressures. As the nature of superconductivity in these materials is still not disclosed, the prospects for a higher Tc are not clear. In contrast the Bardeen-Cooper-Schrieffer (BCS) theory gives a clear guide for achieving high Tc: it should be a favorable combination of high frequency phonons, strong coupling between electrons and phonons, and high density of states. These conditions can be fulfilled for metallic hydrogen and covalent hydrogen dominant compounds. Numerous followed calculations supported this idea and predicted Tc=100-235 K for many hydrides but only moderate Tc~17 K has been observed experimentally. Here we found that sulfur hydride transforms at P~90 GPa to metal and superconductor with Tc increasing with pressure to 150 K at ~200 GPa. This is in general agreement with recent calculations of Tc~80 K for H2S. Moreover we found superconductivity with Tc~190 K in a H2S sample pressurized to P>150 GPa at T>220 K. This superconductivity likely associates with the dissociation of H2S, and formation of SHn (n>2) hydrides. We proved occurrence of superconductivity by the drop of the resistivity at least 50 times lower than the copper resistivity, the decrease of Tc with magnetic field, and the strong isotope shift of Tc in D2S which evidences a major role of phonons in the superconductivity. H2S is a substance with a moderate content of hydrogen therefore high Tc can be expected in a wide range of hydrogen-contain materials. Hydrogen atoms seem to be essential to provide the high frequency modes in the phonon spectrum and the strong electron-phonon coupling.

研究动机与目标

• 探索在高压条件下氢富集化合物实现高温超导的可能性。
• 识别通过强电子-声子耦合与高声子频率使常规BCS超导性达到Tc > 150 K的材料。
• 确定硫氢化物（H2S）在极端压力条件下是否能表现出高Tc超导性。
• 通过同位素取代与磁场依赖性确认超导性的声子起源。

提出的方法

• 使用金刚石对顶砧进行高压实验，将H2S样品压缩至超过150 GPa的压力。
• 测量电阻率随温度和压力的变化，以探测超导转变。
• 施加外部磁场，观察Tc的抑制，以确认超导行为。
• 通过氘代（D2S）实现同位素取代，测量Tc的同位素位移，为声子介导配对提供证据。
• 利用氢化物超导性的理论预测作为实验压力和材料选择的指导。
• 通过电阻率下降至少50倍（与铜相比）分析，表明具有强烈的超导转变。

实验结果

研究问题

• RQ1 在高压条件下，氢基化合物中的常规超导性是否可实现Tc > 190 K？
• RQ2 H2S中的超导性是否如BCS理论所预测的由电子-声子耦合驱动？
• RQ3 当氢被氘取代时，H2S中观测到的Tc是否表现出强烈的同位素效应？
• RQ4 H2S在高压下发生何种结构或化学变化，从而导致超导性？
• RQ5 SHn（n>2）氢化物的形成是否可解释H2S中高Tc超导性的出现？

主要发现

• 在压力超过150 GPa的条件下，H2S在190 K的临界温度下观测到超导性。
• 电阻率下降至少50倍（与铜相比），表明具有强超导转变。
• 外加磁场使Tc降低，证实了该转变的超导本质。
• 在D2S中用氘取代氢后，观测到Tc的显著同位素位移，证实声子在配对中起主导作用。
• 超导性可能与H2S在高压下解离并形成SHn（n>2）氢化物有关。
• 结果与氢化物中高Tc超导性的理论预测一致，特别是由于强电子-声子耦合与高频声子所致。