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-Tc superconductors (HTCS) we introduce a modelfor tight-binding electrons coupled to quasi-critical fluctuations. In thenormal state our model reproduces features the Fermi Surface (FS) observedin ARPES measurements on optimality doped Bi2212, such as the anisotropicsuppression of spectral weight around the M points of the Brillouinzone. The spectral density is characterized by a transfer of spectral weightfrom the main quasiparticle peak to dispersing shadow peaks which originatebranches of a shadow FS. In the superconducting state our model reproducesthe d-wave symmetry of the gap parameter, which results from a balancebetween small-q attraction and large-q repulsion. The gap parameter isenhanced due to cooperative effects of charge and spin fluctuations.