Abstract
Charge-density-waves (CDW) and the related properties of group Vb transition- metal trichalcogetiides are reviewed. These compounds have the common structural unit of the triangular column of the formula MX3, which is the origin of their low-dimensionality.
The unique structure of NbS3 is explained by a property of the Peierls state with the wave vector q=0.5b*. The commensurate periodic lattice distortion observed in TaS3 below 218K is explained in terms of the Fermi surface nesting and the importance of the commensurability energy is stressed. The electrical conductivity below the transition temperature is presented. The conductivity below 100 K is much larger than that extrapolated from above. The contribution of the kinks of CDW (phase solitons) is suggested.
Two kinds of CDW are observed in NbSe3. Both wave vectors are incommensurate to the host lattice. A possible model of discommensuration is presented. The conductivity of NbSe3 remains metallic even below the transition temperature, but it is highly non-Ohmic. The field dependence of the conductivity, the effect of impurities and the high frequency noise in the non-Ohmic region reflecting the motion of CDW. Finally, the relation ship between CDW and the superconductivity is discussed.
