The Cu-3d states in the high-Tc cuprates are often described as a single band of 3dx2−y2 states, with the other four 3d states having about 2 to 3 eV higher energy due to the lower-than-octahedral crystal field at the copper sites. However, excitations to these higher energy states observed with RIXS show indications of strong coupling to doped holes in the 3dx2−y2 band. This relaunches a decades-old question of the possible role of the orbital degrees of freedom that once motivated Bednorz and M\"uller to search for superconductivity in these systems. Here we explore a direction different from the Jahn-Teller electron-phonon coupling considered by Bednorz and M\"uller, namely the interaction between holes mediated by dd excitations.
@article{arxiv.2308.03401,
title = {Can dd excitations mediate pairing ?},
author = {Francesco Barantani and Christophe Berthod and Dirk van der Marel},
journal= {arXiv preprint arXiv:2308.03401},
year = {2023}
}