Superposition of and 3 ? 3 supermodulations in TaS2 probed by scanning tunneling microscopy

We report on a scanning tunnelling microscopy study of TaS2 at 4.2 K. A surface prepared by cleavage showed a superimposed pattern of two types of charge density waveswith 3a 0 × 3a 0 and periodicity, which had never been observed previously. We attribute the superposition to regular stacking of 4H b polytypes or irregular stacking of 2H and 4H b layers.