Normal state pseudogap and (\pi,0) feature in the underdoped high-T_c   cuprates. A microscopical theory
  We show that a simple 2D electron system on a square lattice with hoping between more than nearest neighbors exhibits in the presence of electron spin exchange interaction properties strikingly similar to those observed in the underdoped cuprates It is a normal state pseudogap, its behaviour with doping and T, a form of the spectrum around (0,\pi) etc. The motor is the electronic topological transition which due to two-dimensionality gets new features with respect to well-studied 3D case. 
F. Onufrieva, P. Pfeuty (Laboratoire Leon Brillouin, CE-Saclay,France)