Superconducting fluctuations in overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$

TL;DR

This study provides evidence of persistent superconducting fluctuations in heavily overdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$, challenging the notion that such fluctuations only occur in low-dimensional or disordered systems, and explores their theoretical basis.

Contribution

The paper combines experimental spectroscopic, thermodynamic, and magnetic data with quantum Monte Carlo calculations to reveal superconducting fluctuations in an overdoped cuprate with high carrier density.

Findings

Superconducting fluctuations persist in heavily overdoped Bi2212.

A flat band at ($ackslashpi$,0) enhances phase fluctuations.

Anisotropic band structure influences phase coherence in overdoped cuprates.

Abstract

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 heavily hole-doped cuprate superconductor Bi$_2$Sr$_2$CaCu$_2$O$_{8+\delta}$ ($T_c$ = 66~K) despite the high carrier density. With a sign-problem free quantum Monte Carlo calculation, we show how a partially flat band at ($\pi$,0) can 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.