Raman Evidence for Superconducting Gap and Spin-Phonon Coupling in Superconductor Ca(Fe0.95Co0.05)2As2

TL;DR

This study uses Raman spectroscopy and first-principles calculations to reveal superconductivity-induced phonon renormalization and spin-phonon coupling in Ca(Fe0.95Co0.05)2As2, highlighting the interplay between structural, magnetic, and superconducting transitions.

Contribution

It provides experimental evidence of phonon renormalization linked to superconductivity and theoretical insights into spin-phonon coupling in electron-doped CaFe2As2.

Findings

Phonon mode near 260 cm-1 hardens below Tc, indicating coupling with the superconducting gap.

All Raman active phonons show anomalous temperature dependence from room temperature to Tc.

First-principles calculations reveal short-range stripe antiferromagnetic order and quantify spin-phonon couplings.

Abstract

Inelastic light scattering studies on single crystal of electron-doped Ca(Fe0.95Co0.05)2As2 superconductor, covering the tetragonal to orthorhombic structural transition as well as magnetic transition at TSM ~ 140 K and superconducting transition temperature Tc ~ 23 K, reveal evidence for superconductivity-induced phonon renormalization; in particular the phonon mode near 260 cm-1 shows hardening below Tc, signaling its coupling with the superconducting gap. All the three Raman active phonon modes show anomalous temperature dependence between room temperature and Tc i.e phonon frequency decreases with lowering temperature. Further, frequency of one of the modes shows a sudden change in temperature dependence at TSM. Using first-principles density functional theory-based calculations, we show that the low temperature phase (Tc < T < TSM) exhibits short-ranged stripe anti-ferromagnetic ordering, and estimate the spin-phonon couplings that are responsible for these phonon anomalies.