Observation of a coherent optical phonon in the iron pnictide superconductor Ba(Fe1−xCox)2As2 (x=0.06 and 0.08)

Abstract

We report the observation of a coherent lattice oscillation in a pnictide superconductor. A coherent fully symmetric optical phonon was detected in $\text{Ba}{\left({\text{Fe}}_{1-x}{\text{Co}}_x\right)}_2{\text{As}}_2$ ($x=0.06$ and $x=0.08$) using time-resolved pump-probe reflectivity with 40 fs time resolution. The analysis of the phonon parameters for various excitation fluences reveals no evident difference below and above the critical temperature, suggesting that the $A_{1g}$ mode is not involved in the superconducting phase transition.