Theory of Three-Dimensional Orderings of Charge-Density Waves in 1T-TaX₂ (X: S, Se)

抄録

Three-dimensional structures of charge-density waves in 1T-Ta dichalcogenides are studied on the basis of a phenomenological free energy, in which interlayer couplings up to the second neighbor layer are considered. Special attention is paid to the commensurate (C) and striped discommensurate (DC) states. Several stable stackings are obtained both in the C and striped DC states, where some of them in the C states are found to be disordered. The theory is applied to 1T-TaS₂, on which Tanda et al. have made an X-ray experiment recently. To explain the experimental data a novel model is proposed for the C phase. In addition the structure of the new phase appearing between the C and nearly C phases is discussed from the standpoint of the striped DC state.