Optimization of a Model for the CuO Planes in La2CuO4

Abstract

The results of a previous work, where it was considered the effect of hole doping on a simple model of the CuO₂ planes in La₂CuO₄, are extended. The parameters are adjusted in order to fix the known values of the gap of 2 eV for this material and its dielectric constant of 21. We find again indications of a “hidden” phase transition inside the superconductor dome. The transition is a second order one, and is associated with an energetic coincidence of a ground insulator state (AFA) with an excited paramagnetic state showing a pseudogap (PPG), at a critical point of the hole concentration around x_c = 0.2. We show the evolution as a function of doping of the band structures and the Fermi surface of the system in the phases AFA and PPG. In the zone of low doping, the holes begin to occupy the states located at the Brillouin zone, that in the AFA states have the  strongest antiferromagnetic character. Around the critical doping the results show that in both phases the Fermi surfaces and the  energy spectrum of the filled electronic states tend to coincide.