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From stripe to checkerboard ordering of charge-density waves on the square lattice in the presence of quenched disorder

We discuss the effects of quenched disorder on a model of charge density wave (CDW) ordering on the square lattice. Our model may be applicable to the cuprate superconductors, where a random electrostatic potential exists in the CuO2 planes as a result of the presence of charged dopants. We argue that the presence of a random potential can affect the unidirectionality of the CDW order, characterized by an Ising order parameter. Coupling to a unidirectional CDW, the random potential can lead to the formation of domains with 90 degree relative orientation, thus tending to restore the rotational symmetry of the underlying lattice. We find that the correlation length of the Ising order can be significantly larger than the CDW correlation length. For a checkerboard CDW on the other hand, disorder generates spatial anisotropies on short length scales and thus some degree of unidirectionality. We quantify these disorder effects and suggest new techniques for analyzing the local density of states (LDOS) data measured in scanning tunneling microscopy experiments.