Ab Initio determination of Cu 3d orbital energies in layered copper oxides

TL;DR

This study uses advanced ab initio quantum chemical methods to accurately determine the energies of copper 3d orbitals in layered copper oxides, clarifying their role in high-temperature superconductivity.

Contribution

It introduces a novel ab initio computational approach to precisely measure Cu 3d orbital energies and their trends across different copper oxides.

Findings

Excellent agreement with RIXS measurements for several compounds

Identified trends of orbital energies with apical ligand distances

Confirmed the importance of non-x2-y2 orbitals in low-energy physics

Abstract

It has long been argued that the minimal model to describe the low-energy physics of the high-Tc superconducting cuprates must include copper states of other symmetries besides the canonical x2-y2 one, in particular the z2 orbital. Experimental and theoretical estimates of the energy splitting of these states vary widely. With a novel ab initio quantum chemical computational scheme we determine these energies for a range of copper-oxides and -oxyclorides, determine trends with the apical Cu-ligand distances and find excellent agreement with recent Resonant Inelastic X-ray Scattering measurements, available for La2CuO4, Sr2CuO2Cl2, and CaCuO2.