Diamagnetism and Cooper pairing above Tc in cuprates

In the cuprate superconductors, Nernst and torque magnetization experiments have provided evidence that the disappearance of the Meissner effect at T-c is caused by the loss of long-range phase coherence, rather than the vanishing of the pair condensate. Here we report a series of torque magnetization measurements on single crystals of La2-xSrxCuO4 (LSCO), Bi2Sr2-yLayCuO6 (Bi 2201), Bi2Sr2CaCu2O8+delta, and optimal YBa2Cu3O7. Some of the measurements were taken to fields as high as 45 T. Focusing on the magnetization above T-c, we show that the diamagnetic term M-d appears at an onset temperature T-onset(M) high above T-c. We construct the phase diagram of both LSCO and Bi 2201 and show that T-onset(M) agrees with the onset temperature of the vortex Nernst signal T-onset(nu). Our results provide thermodynamic evidence against a recent proposal that the high-temperature Nernst signal in LSCO arises from a quasiparticle contribution in a charge-ordered state.