Microscopic Study of Domain Structure in Charge Density Wave States in 2H-TaS_1.8Se_0.2

Transition metal dichalcogenides 2H-TaS₂ and 2H-TaSe₂ show charge density wave (CDW) state and superconductivity. It has been reported that elemental substitution of chalcogenide suppresses the CDW and enhances superconductivity. However, how the CDW order is suppressed by the substitution has not been clarified yet. To clarify this, we performed real space observation of the CDW state in the commensurate phase of 2H-TaS_1.8Se_0.2 by scanning tunneling microscopy. The existence of domains separated by walls at which the phase of the CDW shifts was observed. The change in the electronic state on the domain boundaries in 2H-TaS_1.8Se_0.2 was not as drastic as that in 1T-Fe_xTa_1-xS₂. (paper)