Pseudogap Phase in Cuprates: Oxygen Orbital Moments Instead of Circulating Currents

Abstract

Circulating current loops within the cuprate unit cell are proposed to play a key role in the physics of the pseudogap phase. However, main experimental observations motivated by this sophisticated proposal and seemingly supporting the circulating current model can be explained within a simple and physically clear microscopic model. It has been argued that, instead of a well-isolated Zhang-Rice (ZR) singlet 1A 1g, the ground state of the hole center [CuO 4] 5- (cluster analog of Cu 3+ ion) in cuprates should be described by a complex 1A 1g- 1,3B 2g- 1,3E u multiplet, formed by a competition of conventional hybrid Cu 3d-O 2p b 1g(σ)∝ d x2-y2 state and purely oxygen nonbonding O 2pπ states with a 2g(π) and e ux, y(π) symmetry. In contrast to inactive ZR singlet we arrive at several novel competing orbital and spin-orbital order parameters, e. g., Ising-like net orbital magnetic moment, orbital toroidal moment, intra-plaquette's staggered order of Ising-like oxygen orbital magnetic moments. As a most impressive validation of the non-ZR model we explain fascinating results of recent neutron scattering measurements that revealed novel type of magnetic ordering in pseudogap phase of several hole-doped cuprates. © 2012 Pleiades Publishing, Ltd.