Raman scattering study of electron-doped Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ superconductors

TL;DR

This study uses temperature-dependent Raman spectroscopy to analyze phonon behavior in electron-doped Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ superconductors, revealing electron-phonon interactions and constraints on the superconducting gap.

Contribution

It provides the first detailed Raman analysis of phonons in Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$, highlighting electron-phonon coupling effects in the superconducting state.

Findings

Identification of all four symmetry-allowed phonons.

Anomalous hardening of B$_{1g}$ phonon at 222 cm$^{-1}$ at low temperatures.

Evidence of non-zero electron-phonon coupling and an upper limit on the superconducting gap.

Abstract

Temperature-dependent polarized Raman spectra of electron-doped superconducting Pr$_x$Ca$_{1-x}$Fe$_2$As$_2$ ($x \approx 0.12$) single crystals are reported. All four allowed by symmetry even-parity phonons are identified. 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 non-vanishing electron-phonon coupling in the superconducting state and implies that the superconducting gap magnitude $2\Delta_c < 27$meV.