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.
Highlights
In conventional superconductors, the superconducting (SC) transition temperature Tc is controlled by the formation of Cooper pairs via exchange of low-energy pairing bosons of energy Ωp in the BCS paradigm [1]
We investigate the same system near the SC gap opening temperature (Tgap) and the zero-resistivity temperature (Tc) using high-resolution angle-resolved photoemission spectroscopy (ARPES) and 63Cu nuclear magnetic resonance (NMR) [16]
Systematic high-resolution ARPES measurements in this temperature and doping regime are made possible by the recent advance in localized heating method [14,37], which is instrumental to maintain the surface doping level in such superoxygenated samples
Summary
The superconducting (SC) transition temperature Tc is controlled by the formation of Cooper pairs via exchange of low-energy pairing bosons of energy Ωp in the BCS paradigm [1]. Both aspects jeopardize the mean-field premise of the BCS theory, and provide basis for superconducting fluctuations In this regime, it is the condensation of Cooper pairs—establishment of phase coherence—that determines Tc. the normal state of UD and OP cuprates exhibits pseudogap and strange metal behaviors due to strong electronic correlation. Transport [26,27], thermodynamic [13], and single-particle probes [14,28,29,30] all seem to point toward a more three-dimensional, carrier-rich metallic normal state in overdoped cuprates This leads to a widely held belief that the BCS paradigm has a chance to succeed here. (4) Will superconducting phase coherence imprint on the single-particle spectral function in this case?
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