Tight-binding parameters and exchange integrals of Ba_2Cu_3O_4Cl_2

TL;DR

This paper presents band structure calculations and tight-binding parameters for Ba_2Cu_3O_4Cl_2, proposing an extended Hubbard model to describe its magnetic properties, with results aligning well with experimental data for similar compounds.

Contribution

It provides a detailed tight-binding parameterization and exchange integral calculations for Ba_2Cu_3O_4Cl_2, extending understanding of its electronic and magnetic behavior.

Findings

Metallic behavior with two bands crossing the Fermi surface

Small coupling between A- and B-subsystems

Exchange integrals agree with experimental values for Sr_2Cu_3O_4Cl_2

Abstract

Band structure calculations for Ba_2Cu_3O_4Cl_2 within the local density approximation (LDA) are presented. The investigated compound is similar to the antiferromagnetic parent compounds of cuprate superconductors but contains additional Cu_B atoms in the planes. Within the LDA, metallic behavior is found with two bands crossing the Fermi surface (FS). These bands are built mainly from Cu 3d_{x^2-y^2} and O 2p_{x,y} orbitals, and a corresponding tight-binding (TB) model has been parameterized. All orbitals can be subdivided in two sets corresponding to the A- and B-subsystems, respectively, the coupling between which is found to be small. To describe the experimentally observed antiferromagnetic insulating state, we propose an extended Hubbard model with the derived TB parameters and local correlation terms characteristic for cuprates. Using the derived parameter set we calculate the exchange integrals for the Cu_3O_4 plane. The results are in quite reasonable agreement with the experimental values for the isostructural compound Sr_2Cu_3O_4Cl_2.