Phase-fluctuating superconductivity in overdoped La2-xSrxCuO4

In underdoped cuprate superconductors, phase stiffness is low and long-range superconducting order is destroyed readily by thermally generated vortices (and anti-vortices), giving rise to a broad temperature regime above the zero-resistive state in which the superconducting phase is incoherent(1-4). It has often been suggested that these vortex-like excitations are related to the normal-state pseudogap or some interaction between the pseudogap state and the superconducting state(5-10). However, to elucidate the precise relationship between the pseudogap and superconductivity, it is important to establish whether this broad phase-fluctuation regime vanishes, along with the pseudogap(11), in the slightly overdoped region of the phase diagram where the superfluid pair density and correlation energy are both maximal(12). Here we show, by tracking the restoration of the normal-state magnetoresistance in overdoped La2-xSrxCuO4, that the phase-fluctuation regime remains broad across the entire superconducting composition range. The universal low phase stiffness is shown to be correlated with a low superfluid density(1), a characteristic of both underdoped and overdoped cuprates(12-14). The formation of the pseudogap, by inference, is therefore both independent of and distinct from superconductivity.