Superconducting Fluctuations in Overdoped Bi2Sr2CaCu2O8 + δ

Fluctuating superconductivity—vestigial Cooper pairing in the resistive state of a material—is usually associated with low dimensionality, strong disorder, or low carrier density. Here, we report single-particle spectroscopic, thermodynamic and magnetic evidence for persistent superconducting fluctuations in the heavily hole-doped cuprate superconductor Bi2Sr2CaCu2O8þδ(Tc¼66 K) despite the high carrier density. With a sign-problem-free quantum Monte Carlo calculation, we show how a partially flat band at ðπ;0Þcan help enhance superconducting phase fluctuations. Finally, we discuss the implications of an anisotropic band structure on the phase-coherence-limited superconductivity in overdoped cuprates and other superconductors