Fig. 5: CDW domain walls.

a 30 nm × 30 nm area recorded at 4 K, 100 mV, and 20 pA, for 0% Pt doping. The inset shows the Fourier transform of the topography. b Selective inverse Fourier transform of CDW peaks calculated from a. Consistent with previous STM data on pristine samples, the domain wall density is very low. In fact, there are no domain walls in this area. c 30 nm × 30 nm area recorded at 300 mK, 100 mV, and 20 pA, for 0.02% Pt doping. The inset shows the Fourier transform. d Selective inverse Fourier transform of CDW peaks calculated from c. A network of domain walls (seen as short streaks in the principle crystalline directions) is visible. e–h Magnified views of the smaller rectangular areas shown in c and d indicated as 1 and 2 are shown in (e and f) and 2 (g and h), respectively. The red lines indicate CDW domain walls. The orange lines indicate the π-shift between two CDW domains. The phase shift can be seen clearly in e and g by tracking the positions of the atoms across the domain walls.