Persistence of vortexlike phase fluctuations in underdoped to heavily overdoped Bi-2201 cuprates

TL;DR

This study reveals persistent vortexlike phase fluctuations above the superconducting transition in Bi-2201 cuprates, especially in heavily overdoped samples, challenging traditional mean-field theories of superconductivity.

Contribution

It demonstrates that vortexlike phase fluctuations are significant in the overdoped regime, providing new insights into the superconducting transition mechanism in cuprates.

Findings

Enhanced vortexlike fluctuations in heavily overdoped Bi-2201

Suppressed fluctuations near optimal doping

Contrasts with conventional BCS theory

Abstract

The mechanism that controls the superconducting (SC) transition temperature $T_{\mathrm{c}}^{0}$ as a function of doping is one of the central questions in cuprate high-temperature superconductors. While it is generally accepted that $T_{\mathrm{c}}^{0}$ in underdoped cuprates is not determined by the scale of pairing but by the onset of global phase coherence, the role of phase fluctuations in the overdoped region has been controversial. Here, our transport measurements in perpendicular magnetic fields ($H$) on underdoped Bi-2201 reveal immeasurably small Hall response for $T>T_{\mathrm{c}}(H)$ as a signature of SC phase with vortexlike phase fluctuations. We find that the extent of such a regime in $T$ and $H$ is suppressed near optimal doping but becomes strongly enhanced in heavily overdoped Bi-2201. Our results thus show that vortexlike phase fluctuations play an important role in the field-tuned SC transition in the heavily overdoped region, in contrast to conventional mean-field Bardeen-Cooper-Schrieffer description. The unexpected nonmonotonic dependence of phase fluctuations on doping provides a new perspective on the SC transition in cuprates.