Local charge-density-wave structure in 1T-${\mathrm{TaS}}_2$ determined by scanning tunneling microscopy

We have imaged simultaneously the lattice and the charge-density-wave (CDW) superstructure in 1T-${\mathrm{TaS}}_2$ over the temperature range 370–77 K. In the nearly commensurate (NC) phase between 353 and 183 K we find that the CDW occurs not in commensurate domains but with a uniform, incommensurate orientation throughout the crystal surface. Local measurements of the relative angle between the CDW and the underlying atomic lattice failed to find any areas where the local angle was the commensurate angle, in contradiction to the hexagonal-domain NC-phase model of Nakanishi and Shiba. In the nearly commensurate triclinic (T) phase between 223 and 283 K produced when the temperature is increased, we have directly observed CDW discommensurations in agreement with the stretched honeycomb discommensurate T-phase model of Nakanishi and Shiba.