高压下$P6_3/mmc$ ScH $_6$超导电性的量子非谐增强：第一性原理研究
Quantum anharmonic enhancement of superconductivity in $P6_3/mmc$ ScH$_6$ at high pressures: a first-principles study
摘要：
利用第一性原理计算，在随机自洽谐波近似下，分析了100-160 GPa压力范围内，量子离子涨落和晶格非谐性对P63/mmc ScH 6晶体结构和超导电性的影响.我们预测的晶体结构，声子谱，和超导临界温度，这已经在以前的计算中估计不考虑离子波动的晶体结构和假设的晶格动力学的谐波近似的强烈校正。量子离子波动通过增加约5%的氢-氢距离对晶体中存在的H2分子状单元具有很大的影响。根据我们的非谐声子谱，这种结构至少在85 GPa以上是动态稳定的，这比谐波近似给出的压力低45 GPa。与许多超导富氢化合物相反，量子离子效应和随之而来的非谐性倾向于降低超导临界温度，我们的研究结果表明，它可以在P63/mmc SCH 6中增强约15%。我们把临界温度的提高归因于H $_2$类分子单元的拉伸和相应的电子-声子相互作用的增加。我们的研究结果表明，量子离子效应增加超导临界温度在富氢材料与H2单元通过增加氢-氢距离，因此，电子-声子相互作用。
英文摘要：
Making use of first-principles calculations, we analyze the effect of quantum ionic fluctuations and lattice anharmonicity on the crystal structure and superconductivity of P63/mmc ScH6 in the 100-160 GPa pressure range within the stochastic self-consistent harmonic approximation. We predict a strong correction to the crystal structure, the phonon spectra, and the superconducting critical temperatures, which have been estimated in previous calculations without considering ionic fluctuations on the crystal structure and assuming the harmonic approximation for the lattice dynamics. Quantum ionic fluctuations have a large impact on the H2 molecular-like units present in the crystal by increasing the hydrogen-hydrogen distance about a 5%. According to our anharmonic phonon spectra, this structure will be dynamically stable at least above 85 GPa, which is 45 GPa lower than the pressure given by the harmonic approximation. Contrary to many superconducting hydrogen-rich compounds, where quantum ionic effects and the consequent anharmonicity tend to lower the superconducting critical temperature, our results show that it can be enhanced in P63/mmc ScH6 by approximately a 15%. We attribute the enhancement of the critical temperature to the stretching of the H$_2$ molecular-like units and the associated increase of the electron-phonon interaction. Our results suggest that quantum ionic effects increase the superconducting critical temperature in hydrogen-rich materials with H2 units by increasing the hydrogen-hydrogen distance and, consequently, the electron-phonon interaction.
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