From underdoped to overdoped cuprates: two quantum phase transitions.

Several experimental and theoretical studies indicate the existence of a critical point separating the underdoped and overdoped regions of the high-T(c) cuprates' phase diagram. There are at least two distinct proposals on the critical concentration and its physical origin. The first one is associated with the pseudogap formation for p < p, with p≈0.2. The other relies on the Hall effect measurements and suggests that the critical point and the quantum phase transition (QPT) take place at optimal doping, p(opt)≈0.16. Here we have performed a precise density of states calculation and found that there are two QPTs and the corresponding critical concentrations associated with the change of the Fermi surface topology upon doping.