Macroscopic phase separation in overdoped high temperature superconductors

Superconducting diamagnetic properties have been extensively investigated o n Bi2Sr2-xLaxCuO6 and La2-xSrxCuO4 single crystals. Strong evidence for ele ctronic macroscopic phase separation was found in overdoped samples of both systems revealing intrinsic inhomogeneities. It is found that because of t he phase separation in the overdoped region, the criticality of superconduc tivity becomes the same as in the underdoped region albeit very different n ormal state properties between these two regions. This gives a strong indic ation that the superconductivity in underdoped region and overdoped region may have the same underlying mechanism( pairing and phase coherence). Our c onclusion here will have important implication for how we view the high tem perature superconductors.