The Singlet-Triplet Pseudo-Jahn-Teller Centers in Copper Oxides

TL;DR

This paper investigates the complex ground state of hole centers in doped cuprates, focusing on the pseudo-Jahn-Teller effect caused by near-degeneracy of electronic states in CuO4 clusters.

Contribution

It provides a detailed analysis of the pseudo-Jahn-Teller effect in CuO4 centers, highlighting the role of electronic quasi-degeneracy in their ground state.

Findings

Identification of near-degenerate electronic states in CuO4 centers.

Analysis of the pseudo-Jahn-Teller effect driven by this degeneracy.

Implications for the electronic structure of doped cuprates.

Abstract

One of the most exciting features of the hole centers CuO_{4}^{5-} in doped cuprates is an unusually complicated ground state which is the result of the electronic quasi-degeneracy. An additional hole, doped to the basic CuO_{4}^{6-} cluster with the b_{1g} hole can occupy both the same hybrid Cu3d-O2p orbital state resulting in a Zhang-Rice singlet ^1A_{1g} and the purely oxygen e_u molecular orbital resulting in a singlet or triplet ^{1,3}E_u term with the close energies. We present detailed analysis of the (pseudo)-Jahn-Teller effect driven by the near-degeneracy within the (^1A_{1g},^{1,3}E_u)-manifold.