Domain-like Incommensurate Charge-Density-Wave States and the First-Order Incommensurate-Commensurate Transitions in Layered Tantalum Dichalcogenides. II. 2H-Polytype

The incommensurate (I) state of the triple charge-density-wave (CDW) in 2H–TaSe 2 is studied on the basis of McMillan's phenomenological free energy. A sufficiently large number of harmonics is taken into account to describe the I state precisely. Model calculations based on this theory predict the first-order incommensurate-commensurate transition as observed experimentally in 2H–TaSe 2 . The temperature dependence of the order parameters and wave vector in the I state are also calculated. A detailed study is also made on the domain-like structure of the I state whose wave vector is close to that of the commensurate CDW. The pattern of the domain-like structure found for 2H-polytype is different from that for 1T-polytype because of the difference of the commensurability condition between these two polytypes.