Nematic charge fluctuations and electron-phonon coupling in EuFe$_{2}$As$_{2}$ and SrFe$_{2}$As$_{2}$

We study phononic and electronic Raman scattering in the 122 iron pnictide parent compounds EuFe$_{2}$As$_{2}$ and SrFe$_{2}$As$_{2}$. Using polarized Raman spectra we identify all four Raman active phonon modes through the temperature range of 5-300 K from \textit{ab} plane and \textit{ac} plane. Strong interference of the phonon and the electronic continuum is observed in the A$_{g}$ channel below the tetragonal (D$_{4h}$) to orthorhombic (D$_{2h}$) (T-O) phase transition. Quasi-elastic Raman scattering induced by nematic fluctuations observed in the B$_{2g}$ channel in a wide temperature range above the T-O transition. The temperature dependence of the static Raman susceptibility derived from the Raman response $\chi'(0)= \frac{1}{\pi}P\int^{\infty}_{-\infty}\frac{\chi''(\omega)}{\omega}d\omega$ follows a Curie-Weiss like law A(T-T$_{0}$)$^{-1}$, where T$_{0}$ is about 50K below the T-O transition temperature. WLZ acknowledges ICAM support (NSF-IMI grant DMR-0844115), GB, VT and HHK acknowledge support by NSF DMR-1104884 and by U.S. DOE, BES, Award DE-SC0005463, AS acknowledges the support by US DOE, BES, Materials Sciences and Engineering Division.