Infrared Spectroscopic Studies of the Phonon Dynamics in Iron-based Superconductors

The temperature dependent optical reflectivity has been measurement on iron-based superconductors of different families. The optical conductivity has been obtained by using the two-Drude components model. It has been found that the phonons show red- or blue-shift in different samples. Interestingly, the phonon conductivity exhibits a Fano lineshape, suggesting possible coupling between phonon and electrons. Based on the temperature evolution of the lineshape and peak shift, we discuss the possible role played by electron-phonon coupling and spin fluctuation in the occurrence of superconductivity in iron-based superconductors.