(N) model for charge density waves

We generalize the Fukuyama, Lee, Rice model for pinned charge density waves to the case of an (N) vector order parameter and exactly solve the large-N limit. A second order field induced phase transition is observed, from a pinned to a conducting phase, analogously to the scalar case. The pinned region displays an infinite number of metastable equilibrium states while, above threshold, the system has a periodic solution. The model subject to a time dependent external field shows interesting analogies with some features observed in real materials such as the field cooled and the pulse sign memory effects.