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

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 (1)A(1g), the ground state of the hole center [CuO4](5-) (cluster analog of Cu3+ ion) in cuprates should be described by a complex (1)A(1g)-B-1,3(2g)-E-1,3(u) multiplet, formed by a competition of conventional hybrid Cu 3d-O 2p b(1g)(sigma) proportional to d(x2-y2) state and purely oxygen nonbonding O 2p pi states with a(2g)(pi) and e(ux, y)(pi) 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. DOI: 10.1134/S0021364012180087