Anomalous domain structure in 1T-TaS2−xSex observed using scanning tunneling microscopy

On using scanning tunneling microscopy we observed charge-density-wave (CDW) structures in layered compounds 1T-TaS2−xSex (x=0, 0.3, 0.5) at room temperature, and found a new domain structure for the x=0.3 compound. The new domain structure has a mesh-like pattern, in which the domain boundaries are imaged with brighter contrast only at specific sample voltages, implying that the domain structure has an electronic origin. Moreover, the CDW arrangement is irregularly distorted, while its amplitude is spatially unchanged. These features are in clear contrast to those of the hexagonal domains in the x=0 compound, suggesting that the structural transformation with respect to x is not a well-defined phase transition with abrupt disappearance of the hexagonal domains, but a continuous restructuring of CDW. We argue for the mesh-like structure to be a kind of moiré pattern, originating from the local variation of CDW stacking along the c-axis.