Finite band inversion of angular-resolved photoemission in Bi2Sr2CaCu2O8+δ and comparison with optics

Using a maximum entropy technique within a finite band Eliashberg formalism, we extract from recent high accuracy nodal direction angular-resolved photoemission spectroscopy data in optimally doped Bi₂Sr₂CaCu₂O_8+δ (Bi2212) a quasiparticle electron-boson spectral density. Both normal and superconducting states with d -wave gap symmetry are treated. Finite and infinite band results are considered and contrasted. We compare with results obtained for the related transport spectral density, which follows from a similar inversion of optical data. We discuss the implication of our results for quasiparticle renormalizations in the antinodal direction.