Raman phonon anomalies in Sr(Fe1-x\n Co\n x\n )2As2

Abstract

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(Fe1-xCox)2As2 (x=0 and x=0.04) single crystals in the B2g symmetry with respect to 1 Fe unit cell. Upon cooling, we observe a larger split (13 cm-1) of Eg Raman phonon modes pertaining to in-plane Fe and As displacements as the crystals undergo the tetragonal-to-orthorhombic structural phase transition, although a considerable split (9 cm-1) has been reported in Ba(Fe1-xCox)2As2. Furthermore, the splitting of Eg phonon modes is strongly reduced upon doping. We perform an order-parameter analysis revealing a similar doping dependence of Eg phonon splitting as reported in other compounds of 122 family, indicating these phonon anomalies widely exist in 122 iron-based superconductors and might share the same mechanisms.