(a) Phase diagram of the cuprates. At low carrier doping, one has an antiferromagnetic insulator, at higher dopings, a -wave superconductor. is the temperature below which an energy gap appears, marking the pseudogap phase. (b) ARPES intensity at the Fermi energy for a doping of , showing a “Fermi arc.” The red curve encloses an area equal to the oscillation frequency observed in the Hall resistance of underdoped . (c) ARPES intensity at the Fermi energy for a doping of , showing a large Fermi surface instead. The red curve is the prediction of paramagnetic band theory, and its area matches a subsequent oscillation study on overdoped Tl2201.