Small-q electron-phonon interaction and the phase diagram of the cuprates

We have considered the influence of the momentum structure of the effective electron-phonon interaction on the competition of CDW and superconductivity. Keeping exactly the same effective interaction in both channels (which is natural since both SC and CDW are driven by the same electron-phonon interaction), we produce a phase diagram that shows remarkable similarities with that of the cuprates if we associate the pseudogap with a CDW and the doping effect with particle-hole asymmetry. When the electron-phonon interaction is dominated by the small wavectors, we can obtain a d-wave superconducting dome, a CDW that follows the behavior of the pseudogap and more surprisingly, a transition with rising temperature from d-wave CDW to s-wave CDW in the underdoped regime. Our d-wave CDW state at low-T provides the first theoretical explanation of recent thermal transport results that identify the same nodal excitations on both sides of the transition line from the non-superconducting to the superconducting regime [M. Sutherland et al., Phys. Rev. Lett. 94 (2005) 147004]. (c) 2007 Elsevier B.V. All rights reserved.