高压硫化氢：强非谐声子介导超导体
Hydrogen sulphide at high pressure: a strongly-anharmonic phonon-mediated superconductor
摘要：
我们用第一性原理计算方法研究了H-$_2$-S在$P\ge 200$ GPa压力下的结构、振动和超导性质。包含零点能导致H $_2$ S的两种不同的可能离解，即3 H $_2$ S $\to$ 2 H $_3$ S + S和5 H $_2$ S $\to$ 3 H $_3$ S + HS $_2$，其中H $_3$ S和HS $_2$都是金属。对于H $_3$ S，我们在自洽谐波近似下进行非谐效应的非微扰计算，并表明谐波近似强烈高估了电子-声子相互作用（$λ\approx 2.64$在200 GPa）和T $_c$。非谐性使HS键的伸缩模变硬，使H-S键的弯曲模变软。结果，电子-声子耦合被$30\%$（$λ\approx 1.84$，200 GPa）抑制。此外，虽然在谐波水平T $_c$随着压力的增加而减小，但包含非谐波导致T $_c$几乎与压力无关。高压硫化氢是一种强非谐超导体。
英文摘要：
We use first principles calculations to study structural, vibrational and superconducting properties of H$_2$S at pressures $P\ge 200$ GPa. The inclusion of zero point energy leads to two different possible dissociations of H$_2$S, namely 3H$_2$S $\to$ 2H$_3$S + S and 5H$_2$S $\to$ 3H$_3$S + HS$_2$, where both H$_3$S and HS$_2$ are metallic. For H$_3$S, we perform non-perturbative calculations of anharmonic effects within the self-consistent harmonic approximation and show that the harmonic approximation strongly overestimates the electron-phonon interaction ($λ\approx 2.64$ at 200 GPa) and T$_c$. Anharmonicity hardens HS bond-stretching modes and softens H--S bond-bending modes. As a result, the electron-phonon coupling is suppressed by $30\%$ ($λ\approx 1.84$ at 200 GPa). Moreover, while at the harmonic level T$_c$ decreases with increasing pressure, the inclusion of anharmonicity leads to a T$_c$ that is almost independent of pressure. High pressure hydrogen sulfide is a strongly anharmonic superconductor.
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