Phase coherence is considered to govern the superconducting Tc in underdoped cuprates. However on the overdoped side, magnetic and optical evidence of diminishing zero temperature superfluid density are mounting in La2CuO4 cuprates. We combine magnetic and thermodynamic probes with angle-resolved photoemission, and show evidence of superconducting fluctuation substantially above Tc in another heavily overdoped cuprate family Bi2Sr2CaCu2O8+d. With a sign-problem free quantum Monte Carlo calculation, we suggest that the flat band near antinode in can also enhance the thermal fluctuation and reduce the zero-temperature phase stiffness in addition to disorder effects. Sufficient overdoping is also shown to abruptly reduce electron-phonon interaction and strange metal behavior, exemplifying this regime as a promising platform to advance the understanding of the highTc mechanism.
Reference:  He, Chen et al, submitted  He, Hashimoto et al, Science 362, 62 (2018)  Chen, Hashimoto et al, Science 366, 1099 (2019)