Imaging Charge Density Wave Nucleation in NbSe$_{2}$

Understanding the effects of spatial inhomogeneity in complex materials is necessary to achieve a fundamental understanding of their quantum states. NbSe$_{2}$ serves as a clean and relatively simple system for understanding the emergence of one such state -- the charge density wave (CDW) phase. Using variable temperature scanning tunneling microscopy (STM), we visualize the nucleation of CDWs about crystal defects at temperatures well above T$_{CDW}$. The CDW correlation length increases with decreasing temperature, until global order is reached below T$_{CDW}$. We also employ scanning tunneling spectroscopy in order to visualize the energy-dependent, spatial phase of the CDW state. With both topographic and spectroscopic data, we will provide a clear picture of the CDW transition and insight into the microscopic mechanisms at work.