Electron-Phonon Spectral Density of MgB2 from Optical Data, through Maximum Entropy

We use maximum entropy techniques to extract an electron-phonon density from optical data in the normal state at T = 45 K in MgB2. Limiting the analysis to a range of phonon energies below 110 meV which is sufficient to capture all phonon structures we find a spectral function which is in good agreement with that calculated for the quasi two-dimensional sigma-band. Extending the analysis to higher energies up to 160 meV we find no evidence for any additional contributions to the fluctuation spectrum but find that the data can only be understood if the density of states is taken to decrease with increasing energy.