Coherent phonon in superconductor iron pnictide

The role of phonons in high critical temperature superconductivity has been subjected to a large debate and the description of the superconductivity mechanism is still controversial. Recently, the attention of the scientific community has been focused on the new family of iron pnictide superconductors, in which all the degrees of freedom of the crystal, such as spin, lattice and charges, compete giving rise to a fascinating phase diagram. However, such strong correlations make harder to assert on the mechanism of the electrons pair formation. In order to shine light on this key point linked to the occurrence of superconductivity, we study a coherent A$_{1g}$ optical phonon mode in time domain by measuring the transient reflectivity in iron pnictide Ba(Fe$_{1-x}$Co$_x$)$_2$As$_2$ (x=0.06 and 0.08) across the superconducting phase transition [1]. The phonon parameters such as frequency, amplitude and damping time are discussed as a function of both sample temperature and doping. [1] Mansart et al., Pys. Rev. B 80, 172504 (2009)