Revisit the electronic phase diagram of high temperature superconductors: macroscopic phase separation in heavily overdoped regime

Abstract

Superconducting diamagnetic properties have been investigated on a series of La 2− x Sr x CuO 4 single crystals. The superconducting transition curve M( T) evolves systematically from a one-step transition in the underdoped region to a two-step transition in the heavily overdoped regime. The unexpected second transition in the heavily overdoped region can be well explained within the framework of an electronic macroscopic phase separation. The resulting phase due to the phase separation contains many tiny superconducting islands surrounded by non-superconducting good metallic regions. Therefore in the overdoped region, the criticality of superconductivity becomes the same as that in the underdoped region although there are very different normal state properties between these two regions. This gives a strong indication that the superconductivity in the underdoped region and overdoped region may have the same underlying mechanism (pairing and phase coherence).