Quantum Phase Transition in the Magnetic-Field-Induced Normal State of Optimum-Doped High-Tc Cuprate Superconductors at Low Temperatures

A 60 T magnetic field suppresses the superconducting transition temperature T-c in La2-pSrpCuO4 to reveal a Hall number anomaly, which develops only at temperatures below zero-field T-c and peaks at the exact location of p that maximizes T-c. The anomaly bears a striking resemblance to observations in Bi2Sr2-xLaxCuO6+delta, suggesting a normal-state phenomenology common to the cuprates that underlies the high-temperature superconducting phase. The peak is ascribed to a Fermi surface reconstruction at a quantum phase transition near optimum doping that is coincident with the collapse of the pseudogap state.