Strong diamagnetic response and specific heat anomaly above Tc in underdoped La2-xSrxCuO4

By measuring AC susceptibility using a very low amplitude of the AC field (<1 mG) it is shown that underdoped samples of La2-xSrxCuO4, are diamagnetic in a temperature region above Tc up to a temperature T* when the field is directed along the c-axis. At T* a broad step anomaly in the specific heat is inferred through measurements of the elastic constant c33. We suggest that the observed diamagnetism and the anomaly in the elastic constant are associated with the existence of phase incoherent Cooper pairs between Tc and T*