Weak pinning and hexatic order in a doped two-dimensional charge-density-wave system

Scanning tunneling microscopy has been used to characterize the effects of Nm impurities on the incommensurate charge-density-wave (CDW) phase in 1T-${\mathrm{TaS}}_{2}$. Real- and reciprocal-space data indicate that disorder in the CDW is due to dislocations and small random rotations of the CDW. The dislocations destroy translational order; however, calculations show that the orientational order is long range. These results are consistent with weak pinning and suggest the possibility of a hexatic CDW phase. The similarity of our data to results obtained for other two-dimensional systems is discussed.