Effect of dilute, strongly pinning impurities on charge density waves

We study theoretically the effects of strong pinning centers on a charge density wave in the limit that the charge density wave coherence length is shorter than the average inter-impurity distance. An analysis based on a Ginzburg-Landau model shows that long range forces arising from the elastic response of the charge density wave induce a kind of collective pinning which suppresses impurity-induced phase fluctuations leading to a long ranged ordered ground state. The effective correlations among impurities are characterized by a length scale parametrically longer than the average inter-impurity distance. The thermal excitations are found to be gapped implying the stability of the ground state. We also present Monte Carlo simulations that confirm the basic features of the analytical results.