High field phase diagram of cuprates derived from the Nernst effect

Measurements of the Nernst signal in the vortex-liquid state of the cuprates to high fields (33 T) reveal that vorticity extends to very high fields even close to the zero-field critical temperature T-c0. In overdoped La2-xSrxCuO4, we show that the upper critical field H-c2(T) curve does not end at T-c0, but at a much higher temperature. These results imply that T-c0 corresponds to a loss in phase rigidity rather than a vanishing of the pairing amplitude. An intermediate field H*(T) << H-c2(T) is shown to be the field scale for the flux-flow resistivity.