Time-Resolving Monte Carlo Simulation for Structural Fluctuation on Low Temperature Solid Sate Surfaces

我们根据第一性原理计算得到了Si（001）上二聚体体系的模型势（MP）。使用MP，我们在70k下进行了时间分辨动态蒙特卡罗模拟（DMCS）。DMCS的结果很好地再现了70K下Si（001）的时间分辨恒高电流模式STM（TCHC STM）的实验结果。介绍了由电子系统项和电子-振动耦合项组成的哈密顿量。电子-振动耦合常数由振动态的能量和mps得到。利用哈密顿量，得到了二聚体振动的有效温度。结果表明，在20 K以下，当隧穿电流为100 pA时，Te达到250 K左右。在20k以下出现的高Te，基本上解释了为什么在低温下可以观察到对称的STM图像。当衬底温度在20k左右升高时，Te开始急剧下降，其值与60K时的衬底温度几乎相同。这些低Te解释了为什么不对称STM图像在高于50 K的温度范围内恢复。研究了高振动数的二聚体在STM隧道电流的相干激发下在Ge（001）表面的振动。在STM中，局部结构的转变是由隧穿电流相干激发的二聚体振动驱动的，样品偏置电压对激励率的依赖可以通过π^*波段的准维特性半定量地再现。我们证明了一维波段的激发率有一个不随距离STM尖端的距离而衰减的项。在多重分形统计的基础上，通过对二维Ising体系的模拟，明确了表面二聚体体系的主导相干模式。

We obtained the model potential(MP) tor the dimer system on Si(001) based on the first-principles calculations. Using MP, we performed the time-resolving dynamical Monte-Carlo simulation(DMCS) at 70 K. The results from DMCS reproduce well the experimental results the time-resolving constant-height current mode STM(TCHC STM) for Si(001) at 70K. We introduced the Hamiltonian consists of the terms of the electronic system and the elecron-vibration coupling term. The electron-vibration coupling constant is obtained by the energy of the vibrational state and MP. We obtained the effective temperature Te of the dimer vibratio, using the Hamiltonian. We showed that below 20 K, Te reaches about 250 K at 100 pA of the tunneling current. The high Te appearing below 20 K, essentially explains why the symmetric STM images are observed at low temperatures. When the substrate temperature increases around 20 K, Te starts to decrease steeply, and takes the nearly same values as the substrate temperature at 60K. These low Te explains why the asymmetric STM images recover in the temperature range higher than 50 K.The vibration of the dimer on the Ge(001) surface with a high vibrational number excited coherently by tunneling current of STM, was investigated. The transformation of the local structures reported in STM is shown to be driven by the dimer vibration excited coherently by the tunneling current the sample bias voltage dependence on the excitation rate is semiquantitatively reproduced by the quasi-dimensional character of the π^*-band. We show that the excitation rate has a term that does not decay with the distance from the STM tip for the one-dimensional band.On the basis of multifractal statistics, we have clarified the dominant coherent mode of the surface dimer system by the simulation mapped onto the 2D Ising system.