Persistence of vortexlike phase fluctuations in underdoped to heavily overdoped cuprates.

The mechanism controlling the superconducting transition temperature T c 0 as a function of doping is a central question in cuprate high-temperature superconductors. While in underdoped cuprates T c 0 is set by global phase coherence rather than the scale of pairing, the role of superconducting phase fluctuations in the overdoped region remains controversial. Here, transport measurements in perpendicular magnetic fields (H) on Bi2+xSr2-x-yLayCuO6+δ (Bi-2201) cuprates reveal in the underdoped region immeasurably small Hall response for T > Tc(H) as a signature of a superconducting regime with vortexlike phase fluctuations. The extent of this regime in T and H is suppressed near optimal doping but strongly enhanced in heavily overdoped Bi-2201. These results demonstrate that vortexlike phase fluctuations play a key role in the field-tuned superconducting transition in the heavily overdoped region, in contrast to conventional mean-field Bardeen-Cooper-Schrieffer description. Their unexpected nonmonotonic doping dependence provides a new perspective on the superconducting transition in cuprates.