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

Abstract

One of the most exciting features of the hole centers CuO45- 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 CuO46- cluster with the b1g hole can occupy both the same hybrid Cu3d-O2p orbital state resulting in a Zhang-Rice singlet 1A1g and the purely oxygen eu molecular orbital resulting in a singlet or triplet 1,3Eu term with the close energies. We present detailed analysis of the (pseudo)-Jahn-Teller (PJT) effect driven by the near-degeneracy within the (1A1g, 1,3Eu)-manifold.