Raman phonon anomalies in Sr(Fe1-xCox)2As2

Phonon anomalies have been reported in iron-pnictide superconductors indicating a diverse interplay between different orders in the materials.Here,we report Raman scattering measurements on Sr(Fe_1-xCo_x)₂As₂(x=0 and x=0.04)single crystals in the B;symmetry with respect to a 1 Fe unit cell.Upon cooling,we observe a larger split(13 cm;)of Eg Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-toorthorhombic structural phase transition,although a considerable split(9 cm;)has been reported in BaFe_1-xCo_x)₂As₂.Furthermore,the splitting of E;phonon modes is strongly reduced upon doping.We perform an order-parameter analysis revealing a similar doping dependence of E;phonon splitting as reported in other compounds of the 122 family,indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.