Raman scattering study of electron-doped PrxCa1−xFe2As2superconductors

Abstract

Temperature-dependent polarized Raman spectra of electron-doped superconducting Pr${}_{x}$Ca${}_{1\ensuremath{-}x}$Fe${}_{2}$As${}_{2}$ ($x\ensuremath{\approx}0.12$) single crystals are reported. All four even-parity phonons allowed by symmetry are identified. The phonon mode of B${}_{1g}$ symmetry at 222 cm${}^{\ensuremath{-}1}$, 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 $2{\ensuremath{\Delta}}_{c}<27$ meV.