Observation of a coherent optical phonon in the iron pnictide superconductorBa(Fe1−xCox)2As2(x=0.06and 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 $\text{Ba}{({\text{Fe}}_{1\ensuremath{-}x}{\text{Co}}_{x})}_{2}{\text{As}}_{2}$ ($x=0.06$ 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.