Thermodynamic and critical properties of the charge density wave system ErTe3

We present specific heat and ultrasonic measurements on the rare earth tritelluride ErTe3 compound. Thermodynamic anomalies are observed at the upper charge density wave (CDW) phase transition T-CDW1 = 265 K and the second one at T-CDW2 = 155 K. Similar critical behaviors are found at both CDW phase transitions and that we tentatively described in terms of the 3D XY model. Different anisotropic stress dependences partial derivative T-CDW1/partial derivative sigma(ii) and partial derivative T-CDW2/partial derivative sigma(ii) are found at the two successive CDW phase transitions. Magnitude of the elastic constant anomalies at T-CDW2 is ten times smaller than that at T-CDW1. Anomalies in the elastic constants at the upper CDW T-CDW1 exhibit two dimensional features in the layer planes while in contrast a three dimensional behavior is observed at T-CDW2.