Controlling Orbital Ordering of Intergrowth Structures with Flat [Ag(II)F2] Layers to Mimic Oxocuprates(II)

TL;DR

This study uses DFT calculations to design new flat [AgF2] layers mimicking [CuO2] in oxocuprates, predicting high superconducting temperatures and exploring structural and electronic properties of intergrowth compounds.

Contribution

It introduces a novel pathway to create flat [AgF2] layers with potential high-temperature superconductivity, supported by stability and electronic structure predictions.

Findings

Gigantic superexchange constants up to -256 meV.

Predicted superconducting critical temperature of 200 K at optimal doping.

Structural factors influencing flatness and orbital ordering are identified.

Abstract

Based on the Density Functional Theory calculations, we propose a new pathway toward compounds featuring flat [AgF2] layers which mimic [CuO2] layers in high-temperature oxocuprate superconductor precursors. Calculations predict the dynamic (phonon) and energetic stability of the new phases over diverse substrates. For some compounds with ferro orbital ordering, we find a gigantic intrasheet superexchange constant of up to minus 211 meV (DFT+U) and minus 256 meV (SCAN), calculated for hypothetical (CsMgF3)2KAgF3 intergrowth. Semiempirical calculations show that at optimum doping, the expected superconducting critical temperature should reach 200 K. The partial substitution of K+ with Ba2+ leads to noticeable electron doping of [AgF2] sublattice, as revealed by progressive population of the Upper-Hubbard band. On the other hand, modest 10 to 15% hole-doping through partial substitution of Mg2+ with Li+, primarily leads to the depopulation of p(z) orbitals of apical F atoms. We also find structures with an undesired antiferrodistortive structural ordering and discuss the structural factors that determine the transition from buckled to flat planes and from different types of orbital ordering using Landau theory of phase transitions.