Shadow bands, gap and pseudogaps in high-Tc superconductors

Within the framework of the Charge Density Wave Quantum Critical Point (CDW-QCP) scenario for high-T-c superconductors (HTCS) we introduce a model for tight-binding electrons coupled to quasi-critical fluctuations. In the normal state our model reproduces features the Fermi Surface (FS) observed in ARPES measurements on optimality doped Bi2212, such as the anisotropic suppression of spectral weight around the M points of the Brillouin zone. The spectral density is characterized by a transfer of spectral weight from the main quasiparticle peak to dispersing shadow peaks which originate branches of a shadow FS. In the superconducting state our model reproduces the d-wave symmetry of the gap parameter, which results from a balance between small-q attraction and large-q repulsion. The gap parameter is enhanced due to cooperative effects of charge and spin fluctuations.