Optimization of a model for the CuO planes in La2CuO4

TL;DR

This paper extends a model of CuO2 planes in La2CuO4 to include doping effects, revealing a hidden second-order phase transition near a critical doping level, with implications for understanding the material's electronic phases.

Contribution

It introduces parameter adjustments to match experimental gap and dielectric constant, and uncovers a hidden phase transition associated with doping in the model.

Findings

Identification of a second-order phase transition at critical doping xc=0.2.

Evolution of Fermi surface and band structure with doping.

Coincidence of Fermi surfaces in different phases near critical doping.

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 with the objective 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 beneath 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 xc=0.2. The evolution as a function of doping of the band structures and the Fermi surface of the system in the phases AFA and PPG, is shown. In the zone of low doping, the holes begin to occupy the states located at the mid of the sides of 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.