Antiferromagnetic phase diagram of the cuprate superconductors

Abstract

Taking the spin-fermion model as the starting point for describing the cuprate superconductors, we obtain an effective nonlinear sigma-field hamiltonian, which takes into account the effect of doping in the system. We obtain an expression for the spin-wave velocity as a function of the chemical potential. For appropriate values of the parameters we determine the antiferromagnetic phase diagram for the YBa 2 Cu 3 O 6+x compound as a function of the dopant concentration in good agreement with the experimental data. Furthermore, our approach provides a unified description for the phase diagrams of the hole-doped and the electron doped compounds, which is consistent with the remarkable similarity between the phase diagrams of these compounds, since we have obtained the suppression of the antiferromagnetic phase as the modulus of the chemical potential increases. The aforementioned result then follows by considering positive values of the chemical potential related to the addition of holes to the system, while negative values correspond to the addition of electrons.

Effective potential for emergent Majorana fermions in superconductor systems

“…Although described by the effective potential of Majorana fermions, this result was expected since the present work consists of an analysis of an electronic system, with ∆ being the same parameter in both effective potentials, Majorana fermions, and electrons. Furthermore, it also corresponds to the same results obtained by the spin fermion model, a candidate to explain how high-T c superconductivity emerges in CuO planes of cuprates systems [21][22][23]. The fact that these gap equations are equivalent and both systems are (quasi-)bidimensional suggests the existence of a natural emergence of Majorana fermions in the CuO planes in cuprates.…”