Fermi surface and photoemission lineshape of incommensurate CDW systems

We study the single-particle spectra of a model which shows an incommensura te charge-density wave (CDW) instability arising from the competition betwe en phase separation and long-range Coulomb interactions. Starting from an o pen Fermi surface we find that the resulting CDW is oriented along the (1,0 )- and (or) (0,1)-direction which (besides a purely one-dimensional structu re) allows for a two-dimensional "eggbox type" charge modulation. This lead s to a substantial enhancement of the van Hove singularities and the spectr al weight of Fermi surface states near the M-points tends to be suppressed. Remarkably, a leading edge gap arises near these points, which, in the egg box case, leaves finite arcs of the Fermi surface gapless. Extending this a pproach to the inclusion of dynamic incommensurate CDW fluctuations in the superconducting state we calculate the photoemission lineshape which agrees well with experimental data of underdoped Bi2212 compounds.