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

A 60 T magnetic field suppresses the superconducting transition temperature Tc in La_2-pSrₚCuO₄ to reveal a Hall number anomaly, which develops only at temperatures below zero-field Tc and peaks at the exact location of p that maximizes Tc. The anomaly bears a striking resemblance to observations in Bi₂Sr_2-xLaₓCuO_6+δ, 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.