Raman scattering study of electron-doped PrxCa1-xFe2As2 superconductors

Temperature-dependent polarized Raman spectra of electron-doped superconducting PrxCa1-xFe2As2 (x approximate to 0.12) single crystals are reported. All four even-parity phonons allowed by symmetry are identified. The phonon mode of B-1g symmetry at 222 cm(-1), which is associated with the c-axis motion of Fe ions, is found to exhibit an anomalous frequency hardening at low temperatures, that signals nonvanishing electron-phonon coupling in the superconducting state and implies that the superconducting gap magnitude 2 Delta(c) < 27 meV.