Real-space fluctuations of effective exchange integrals in high-Tc cuprates

TL;DR

This study uses ab-initio calculations to show how local doping atom distributions in high-Tc cuprates significantly influence magnetic exchange interactions and orbital energies, correlating with observed inhomogeneities.

Contribution

It reveals the strong dependence of magnetic and orbital properties on local dopant arrangements, highlighting an extrinsic origin of inhomogeneities in high-Tc cuprates.

Findings

Exchange interactions vary with dopant distribution

Orbital energy fluctuations cause charge inhomogeneities

Results align with experimental inhomogeneity observations

Abstract

We present ab-initio calculations of effective magnetic exchange, $J$, as well as Hubbard parameters ($t$, $U$ and $\delta \varepsilon$) as a function of the local distribution of doping atoms for the high-$T_c$ superconducting $\rm (Ca_xLa_{1-x})(Ba_{1.75-x}La_{0.25+x})Cu_3O_y$ family. We found that both the exchange and the energies of the magnetic orbitals are strongly dependant on the local dopant distribution, both through the induced modification of the apical oxygen location and of the induced local electrostatic potential. The $J$ real-space map, for a random distribution of dopants, positively compares with observed STS gap inhomogeneity maps. Similarly, the orbital energy fluctuations induce weak charge inhomogeneities on copper sites, that can be positively compared with the observed LDOS inhomogeneities. These results clearly support an extrinsic origin of both the gap inhomogeneities and LDOS.