hybridization integral and energy barrier in high-temperature superconductor cuprates

Question

I am reading an article about high-temperature superconducting cuprates. It was saying because the hybridization integral $t_{dp}$ is much smaller than the energy barrier E$_p$-E$_d$, the electrons in the undoped compounds form localized moments on the Cu sites.

I am a bit confused about this part. if the hybridization integral is lower in energy, then electrons would favor to occupy the hybridized band, which has components from both Cu d-states and Oxygen p-states. Why it says the electrons localize on Cu sites?

Any help would be appreciated. Thank you very much!

Answer 1

These are not the only parameters that matter. It starts with the on-site Coulomb interaction $U_{dd}$, which would lead to a Mott insulator with localized moments on Cu $3d^9$ ions, because of the huge energy barrier against creating $3d^8$ and $3d^{10}$ states.

But one needs to consider that there may be excitations at lower energies that involve the ligand bands. This led to the Zaanen-Sawatzky-Allen classification of such compounds according to the nature of the band gap.

It is not quite clear what the paper that you read is about. It may be talking about where the holes induced by doping the cuprate are.