Self Energy and Fluctuation Spectra in Cuprates: Comparing Optical and Photoemission Results

We compare efforts to extract self energies and fluctuation spectra of the cuprates using optical and photoemission techniques. The fluctuations have contributions from both the coherent and incoherent parts of the band, which are spread over the full bare bandwidth of >2eV. Many experimental studies concentrate on the coherent part of the band and hence miss higher energy fluctuations. Our study establishes the universal presence of high energy bosonic fluctuations across various spectroscopies as a key ingredient in the high temperature superconducting cuprates.