Stripes, vibrations, and superconductivity

We propose a model of a spatially modulated collective charge state (CCS) of superconducting cuprates. [For a shorter version of this work, see A. H. Castro Neto, in Proceedings of the MTSC 2000 [J. Supercond. 13, 913 (2000)].] The regions of higher carrier density (stripes) are described in terms of one-dimensional (1D) interacting fermions and the regions of lower density as a two-dimensional (2D) interacting bosonic gas of d_x²-y² hole pairs. The interactions among the elementary excitations are repulsive and the transition to the superconducting state is driven by decay processes. Vibrations of the CCS and the lattice, although not participating directly in the binding mechanism, are fundamental for superconductivity. The superfluid density and the lattice have a strong tendency to modulation with wave vectors (π/a,0) and (0,π/a) implying a still unobserved dimerized stripe phase in cuprates. The phase diagram of the model has a crossover from 1D to 2D behavior and a pseudogap region where the amplitude of the order parameters are finite but phase coherence is not established. We discuss the nature of the spin fluctuations and the unusual isotope effect within the model.