Schematic phase diagram of a cuprate superconductor plotted as a function of the applied field (H) and temperature (T). The field-dependent crossover temperature TM bounding the vortex liquid region is shown as a green dashed line. The superconducting phase is bounded by the solid red line. The region in which evidence of unusual, possibly 2D superconducting behavior is found in some cuprates is indicated by the dark blue region above Tc. T* denotes the crossover between the “bad metal” phase—so called because in this state conventional transport theory breaks down—and the pseudogap phase, which recent experiments suggest may be related to the onset of electron-nematic order [2, 11].