Eliashberg analysis of Bi2Sr2CaCu2O8+δO8+δ intrinsic tunneling spectra

• Temperature-dependent intrinsic tunneling spectra of Bi2Sr2CaCu2O8+δ are analyzed.
• The pairing spectral function, the self energy, and the gap function are obtained.
• Spin-fluctuation-mediated pairing is demonstrated.

Tunneling spectra of Bi2Sr2CaCu2O8+δO8+δ intrinsic Josephson junctions with different doping are analyzed and reproduced using a d  -wave Eliashberg formalism in a wide temperature range below TcTc, from which the pairing glue spectral function α2F(Ω)α2F(Ω) composed of a low-energy resonance peak and a high-energy broad spectrum is obtained. As temperature increases toward TcTc, the resonance peak shows continuous decrease both in energy and in height while the broad spectrum slightly increases in height. The calculated coupling constant demonstrates an important role for pairing by the broad spectrum that originates from spin fluctuations. The gap function extracted from the analysis bears a close resemblance to the recent Hubbard and t–J model simulations. We discuss the limitations of the d-wave Eliashberg approach used in our analysis.