Origin of magnetoresistance anomalies in antiferromagnetic YBa2Cu3O6+x

Specific d-wave angular dependence of the in-plane magnetoresistance in antiferromagnetic tetragonal YBa2Cu3O6+x (x∼0.3) on the orientation of the external magnetic field within the (a,b) plane is assigned to the effective hole transport through the low-lying excited pure oxygen doublet O2peu state in CuO4 plaquette, rather than the ground b1g(dx2−y2) state. The external magnetic field is believed to determine the orientation of the strong exchange field for the spin-triplet b1geu:3Eu state of the hole CuO4 center and owing to the spin–orbit coupling results in a specific orbital polarization of the Eu doublet. Namely, this gives rise to the spatial d-wave like anisotropy of the hole transport. The experimental data allow to estimate the parameter of the effective spin Hamiltonian.