Direct visualization of the periodic displacement of Ta atoms in the commensurate charge density wave phase of 1T-TaSe2 in real space

In 1T-TaSe2, annular dark-field scanning transmission electron microscopy (ADF-STEM) of the commensurate charge density wave (CCDW) phase shows the periodic image contrast superimposed on the atomic columns. The periodicity of the image contrast is consistent with the superlattice formed by the periodic displacement of Ta atoms by the CCDW. Comparing the ADF-STEM with simulated images shows that the image contrast is formed by the displacement of Ta atoms. This result means that the displacement of Ta atoms by the CCDW is directly observed in real space and suggests that a coherent CDW forms on every layer of 1T-TaSe2.