Molecular orbital excitations in cuprates

TL;DR

This study uses resonant inelastic x-ray scattering to investigate how molecular orbital excitations in cuprates vary with copper-oxygen bond length, revealing stronger bond-length dependence of electronic properties than predicted.

Contribution

It provides new experimental insights into the bond-length dependence of charge-transfer excitations and hopping integrals in cuprates, challenging existing tight-binding models.

Findings

Excitation energy increases with decreasing bond length.

Dispersion of excitations becomes more pronounced at shorter bond lengths.

Bond-length dependence of t_pd is stronger than tight-binding predictions.

Abstract

We report resonant inelastic x-ray scattering studies of electronic excitations in a wide variety of cuprate compounds. Specifically, we focus on the charge-transfer type excitation of an electron from a bonding molecular orbital to an antibonding molecular orbital in a copper oxygen plaquette. Both the excitation energy and the amount of dispersion are found to increase significantly as the copper oxygen bond-length is reduced. We also find that the estimated bond-length dependence of the hopping integral t_pd is much stronger than that expected from tight-binding theory.