Abstract
The 423K phase transition of CsCuCl3 is attributed to a cooperative Jahn-Teller effect. Using results of the group-theoretical analysis of phonon modes, it is shown that helical atomic displacements in the low-temperature phase can be represented by a suitable linear combination of the polarization vectors of the Jahn-Teller active E1 modes with wavevectors q=+or-(0 0 2 pi /3c) of the high-temperature phase. The transition may be regarded as an order-disorder limit of the pseudospin-phonon coupled-type phase transition. Formation of the helical structure through the first-order transition is explained on the basis of the group-theoretical formulation of the Landau theory of phase transitions.