Study of Motion of Charge-Density-Wave with Tunnelig Microscope

为了研究电荷密度波(CDW)的滑移现象，我们进行了电学测量和扫描隧道显微镜(STM)观察。在电学测量中，我们系统地测量了K@&gt；D20.3@&gt；D2MoO_3的电导率、滑移阈值场、窄带噪声以及随温度和外加静水压力变化的暂态电压振荡。用连续波相位相关长度的变化解释了阈值光场的行为，证实了弱钉扎机制。窄带噪声和暂态电压振荡的结果表明，随着速度调制相位相关长度的增加，CDW开始滑移，随着速度相关性的降低，CDW向稳态滑移转变。在STM测量中，我们首先搭建了工作在低温区的STM装置。利用该装置，我们尝试观察了K_&lt；0.3&gt；MoO_3中CDW引起的超晶格结构的图像，但没有获得清晰的原子图像和超结构。究其原因，主要是样品表面的污染，气体吸收的控制是今后需要解决的问题。同时，我们观察到在偏置电流作用下，隧道电流的光谱有一个尖锐的峰。这一峰值被认为是随着CDW的滑动运动，隧道尖端与样品表面原子之间的距离发生周期性调制而产生的。这是首次在样品表面直接观测到滑动的CDW。证实了CDW在样品表面的滑动速度比在样品内部的滑动速度快。

We have done the electric measurement and the STM (Scanning Tunneling Microscope) observation to investigate the sliding of CDW (Charge Density Wave).In the electric measurement, we measured the electric conductivity, the threshold field for sliding, the narrow band noise and the transient voltage oscillation in K@>D20.3@>D2MoO_3 with varying the temperature and the applied hydrostatic pressure systematically. The behavior of threshold field was explained with the variation of phase correlation length of CDW and these results confirmed the weak pinning mechanism. The results of the narrow band noise and the transient voltage oscillation indicated that the CDW begins to slide with the long correlation length of phase of velocity modulation and changes to the stationary sliding state with decreasing the velocity correlation. Then, the CDW behaves as a rigid body at the beginning of sliding and as a more deformable one at the stationary sliding state.In the STM measurement, at first we constructed the STM apparatus operating in the low temperature region. Using this apparatus, we tried to observe the image of super-lattice-structure due to the CDW in K_<0.3>MoO_3, but didn't succeed to obtain the atomic image nor the super-structure clearly. The reason is mainly attributed to the contamination of sample surface and the control of the gas absorption is the future problem. While, we observed a sharp peak in the spectra of tunneling current under a bias current. This peak was considered to be generated by the periodic modulation of the distance between the tunneling tip and the surface atom of sample with the sliding motion of CDW. This is the first direct observation of sliding CDW at the sample surface. It was confirmed that the CDW is sliding faster at the surface than the inside of sample.