Visualization of Charge-Density-Wave Reconstruction and Electronic Superstructure at the Edge of Correlated Insulator 1T-NbSe 2 .

Edges of low-dimensional quantum systems have profound effects on both fundamental research and device functionality. Real-space investigation of the microscopic edge structures and understanding the edge-modulated electronic properties are of great essence. Here we report the nanoscale structural reconstruction at the atomically sharp edge of a charge-density-wave (CDW) correlated insulator 1T-NbSe 2 and the induced electronic properties. We find the CDW unit cells at the edge of single layer (SL) 1T-NbSe 2 evolve from the well-defined CDW order in bulk and spontaneously reconstruct into the quartet along the edge. Moreover, we capture an anomalous electronic superstructure along the edge, the periodicity of which is four times that of ordinary CDW lattice. Our findings provide a way to design the one-dimensional electronic superstructure in 2D quantum materials.