A new disorder-driven roughening transition of charge-density waves and flux-line lattices

We study the competition between pinning of a charge-density wave by random distributed impurities and a periodic potential of the underlying crystal lattice. In d = 3 dimensions, we iind for commensurate phases of order p > p(c) approximate to 6/pi a disorder-driven continuous roughening transition from a "flat" phase with translational long-range order to a "rough" glassy phase with quasi-long-range order. Critical exponents are calculated in a double expansion in mu = p(2)/p(c)(2) - 1 and epsilon = 4 - d and fulfill the scaling relations of random field models. Implications for flux-line lattices in high temperature superconductors are briefly discussed.