Low-Field Hall effect, Pseudogap and Magnetic Textures in the Bi₂Sr₂CaCu₂O_8+x Superconductor

We report on low-field Hall effect experiments in Bi2Sr2CaCu2O8+x single crystals with different carrier concentrations. The Hall coefficient is described as a sum of an ordinary term and an anomalous term. The temperature-dependent anomalous term has the form of a cutoff law where the relevant parameter is the doping-dependent pseudogap temperature, T-& lowast; (p), suggesting that the pseudogap boundary is a crossover phenomenon rather than a thermodynamic phase transition. Field-induced spin chiralities accompanied by loop orbital currents flowing in the Cu-O(2 )cell units are proposed as the microscopic origin of the anomalous term. We justify the cutoff law that effectively describes the temperature dependence of the anomalous term as resulting from a Griffiths-type cluster arrangement, where spins are antiferromagnetically coupled. The strong doping dependence of both the ordinary and anomalous terms suggests the occurrence of a Fermi surface reconstruction for carrier concentrations slightly below that of the optimum T-c.