Fermi Surface and gap parameter in high-Tc superconductors: the Stripe Quantum Critical Point scenario

Abstract

We study the single-particle spectral properties of electrons coupled to quasicritical charge and spin fluctuations close to a stripe-phase, which is governed by a Quantum Critical Point near optimum doping. We find that spectral weight is transferred from the quasiparticle peak to incoherent dispersive features. As a consequence the distribution of low-laying spectral weight is modified with respect to the quasiparticle Fermi surface. The interplay of charge and spin fluctuations reproduces features of the observed Fermi surface, such as the asymmetric suppression of spectral weight near the M points of the Brillouin zone. Within the model, we also analyze the interplay between repulsive spin and attractive charge fluctuations in determining the symmetry and the peculiar momentum dependence of the superconducting gap parameter. When both spin and charge fluctuations are coupled to the electrons, we find $d_{x^2-y^2}$-wave gap symmetry in a wide range of parameter. A crossover $d$- vs $s$-wave symmetry of the gap may occur when the strength of charge fluctuations increases with respect to spin fluctuations.