论文标题
离子波动在NBSE $ _2 $的电荷密度波过渡中的弱维依赖性和主导作用
Weak Dimensionality Dependence and Dominant Role of Ionic Fluctuations in the Charge-Density-Wave Transition of NbSe$_2$
论文作者
论文摘要
已经报道了关于2H NBSE $ _2 $中电荷密度波过渡的维度效应的矛盾实验。同时通过分子束外截图生长的单层扫描隧穿实验测量单层中的电荷密度波过渡温度，类似于大容量，大约33 K（约33 K），拉曼实验exfoliated样品的exfoliated样品观察到通过使用非局限性的温度来实现的温度，从而可以通过使用量的温度来实现量度，以实现Anhmarson的频谱，我们可以计算出来，我们可以计算出量度的范围，我们可以计算出我们的音量，我们可以计算出我们计算的，我们可以计算出我们计算的，我们可以计算出我们计算的，我们会算起我们计算的，我们可以计算出我们的温度。无论是散装还是单层。在这两种情况下，电荷密度的波过渡温度均被估计为驱动结构不稳定性的模式的声子能量消失的温度。与实验相当吻合，在散装中获得的过渡温度约为59 K，并且在单层极限中仅略有增加到73 K，显示了过渡对维度的弱依赖性。环境因素可以激发实验报告的过渡温度之间的分歧。我们的分析还证明了电荷密度波顺序融化中离子波动比电子波动占主导地位。
Contradictory experiments have been reported about the dimensionality effect on the charge-density-wave transition in 2H NbSe$_2$. While scanning tunnelling experiments on single layers grown by molecular beam epitaxy measure a charge-density-wave transition temperature in the monolayer similar to the bulk, around 33 K, Raman experiments on exfoliated samples observe a large enhancement of the transition temperature up to 145 K. By employing a non-perturbative approach to deal with anharmonicity, we calculate from first principles the temperature dependence of the phonon spectra both for bulk and monolayer. In both cases, the charge-density-wave transition temperature is estimated as the temperature at which the phonon energy of the mode driving the structural instability vanishes. The obtained transition temperature in the bulk is around 59 K, in rather good agreement with experiments, and it is just slightly increased in the single-layer limit to 73 K, showing the weak dependence of the transition on dimensionality. Environmental factors could motivate the disagreement between the transition temperatures reported by experiments. Our analysis also demonstrates the predominance of ionic fluctuations over electronic ones in the melting of the charge-density-wave order.
