How Superconductivity Dies at High Hole Doping in Cuprates

The phase diagram for cuprate superconductors, plotted as temperature vs. hole concentration p, is very well known. At p = 0, one has an antiferromagnetic insulator. For finite doping, superconducting order appears above a threshold of p ~ 0.05, with the superconducting transition temperature rising continuously to a maximum for p ~ 0.16, beyond which it gradually drops toward zero. At smaller p, anomalous normal-state properties associated with doping holes into a correlated insulator appear below a crossover temperature that tends toward zero at p* ~ 0.19. This point is frequently suggested to be a quantum critical point, in which case the superconducting dome might be associated with a pairing mechanism associated with quantum critical fluctuations; however, no one has ever convincingly identified an order parameter that becomes quantum critical at p*. I will give a different perspective on the phase diagram. The superconductivity is strong in the doping range where strong electron correlations exist, as evidenced by the presence of antiferromagnetic spin excitations. At large p, spin correlations disappear along with the superconductivity. I argue that, in the absence of disorder, the loss of superconductivity would occur as a sharp transition at p*. Because of intrinsic disorder, the superconductor-to-metal transition occurs gradually with p. I will support this story with a variety of experimental results for La2-xSrxCuO4.