Tomography scan of charge density wave in NbSe₂

Charge density wave (CDW) resulting from a periodic distortion in the lattice creates new orders beyond the original lattice. In 2H-NbSe₂, the 3×3 charge order appears in two-dimensional (2D) layers. Although CDW can be observed by different techniques, the spatial distribution within a 2D layer has never been systematically visualized. Here, by using scanning tunneling microscopy (STM) and density functional theory (DFT), we monitored the evolution of CDW along the c-axis and realized a nearly tomography scan of CDW of the topmost layer. The results show that the appearance of the CDW varies while tuning the tunneling current and undergoes a transition from the outermost Se to Nb orbitals. The calculation of orbital charge distributions shows that both CDW intensity modulation and the transition are strongly correlated with the distribution of Se 4p orbitals and Nb 4d orbitals.