论文标题
基于第一原理计算 -
Transition Temperature of Superconductivity in Sodium Tungsten Bronze -Theoretical Study Based on First-principles Calculations-
论文作者
论文摘要
使用第一原理计算，我们检查了钠钨青铜器中超导性的过渡温度$ t _ {\ rm c} $（na $ _x $ _x $ wo $ _3 $，其中$ x $等于或小于unity）。尽管$ t _ {\ rm c} $相对较低$ t _ {\ rm c}（<\ sim 3 {\ rm k}）$，但有趣的是，在$ \ sim 0.2 <x <x <x <\ sim 0.4 $中，已经在实验上观察到了其对$ x $的特征指数依赖性。根据$ t _ {\ rm c} $的McMillan方程，包括等离子的效果，我们成功地复制了$ t _ {\ rm c} $的绝对值及其$ x $依赖性。我们还发现，等离子体效应对于$ t _ {\ rm c} $的估计以及声子至关重要。由于计算出的$ t _ {\ rm c} $即使对于$ x <\ sim 0.1 $，也可能不超过$ \ sim 20 $ k，因此通常可以通过通常的声子（包括Plasmon效应）来解释以低$ t _ {\ rm c} $的超导性。另一方面，高达90 k的高$ t _ {\ rm c} $，在最近的实验中，在$ x \ sim 0.05 $的表面上找到，无法通过我们的结果来解释。这种差异表明，需要另一种机制来阐明高$ t _ {\ rm c} $ na $ _x $ wo $ _3 $的超导性。
Using first-principles calculations, we examine the transition temperature $T_{\rm c}$ of superconductivity in sodium tungsten bronze ( Na$_x$WO$_3$, where $x$ is equal to or less than unity ). Although $T_{\rm c}$ is relatively low $T_{\rm c}( <\sim 3 {\rm K})$, it is interesting that its characteristic exponential dependence on $x$ has been experimentally observed at $\sim 0.2 < x < \sim 0.4$. On the basis of the McMillan equation for $T_{\rm c}$ including the effect of plasmons, we succeed in reproducing the absolute values of $T_{\rm c}$ and its $x$ dependence. We also find that the plasmon effect is crucial for the estimation of $T_{\rm c}$ as well as phonons. Since the calculated $T_{\rm c}$ may not exceed $\sim 20$ K even for $x <\sim 0.1$, the superconductivity at a low $T_{\rm c}$ can be interpreted by the usual phonon mechanism, including the plasmon effect. On the other hand, a high $T_{\rm c}$ up to about 90 K, which is found on the surface of a Na$_x$WO$_3$ system at $x\sim 0.05$ by recent experiments, cannot be explained by our results. This discrepancy suggests that another mechanism is required to clarify the nature of the high-$T_{\rm c}$ superconductivity of Na$_x$WO$_3$.
