Elastic properties at the charge density wave phase transitions in TbTe3, ErTe3 and HoTe3

Rare earth tritelluride TbTe3, ErTe3 and HoTe3 exhibit two successive charge density wave phase transitions T-CDW1 and T-CDW2. The transition to the incommensurate phase at T-CDW2 is reflected in the longitudinal elastic stiffness components C-11 and C-33. In the incommensurate phase below T-CDW2 the longitudinal stiffness components C-11, C-33 are augmented by a contribution from quartic anharmonic interaction with the onset of the incommensurate ordering. The temperature dependences of the elastic constants C-11, C-33 are shown to follow a T-2 law. The mechanism for the lower CDW phase transition is significantly different from that at the upper CDW phase transition.