Phonon Anomalies, Orbital-Ordering and Electronic Raman Scattering in iron-pnictide Ca(Fe0.97Co0.03)2As2: Temperature-dependent Raman Study

TL;DR

This study investigates temperature-dependent phonon and electronic Raman scattering in Ca(Fe0.97Co0.03)2As2, revealing strong spin-phonon coupling, orbital level splitting, and magnetic excitations across structural and magnetic transitions.

Contribution

It provides detailed insights into phonon anomalies, orbital ordering, and magnetic excitations in iron-pnictide Ca(Fe0.97Co0.03)2As2 through comprehensive Raman spectroscopy analysis.

Findings

Phonon mode frequencies increase sharply below Tsm.

Linewidths of Raman modes broaden anomalously below Tsm.

Orbital level splitting increases as temperature decreases below Tsm.

Abstract

We report inelastic light scattering studies on Ca(Fe0.97Co0.03)2As2 in a wide spectral range of 120-5200 cm-1 from 5K to 300K, covering the tetragonal to orthorhombic structural transition as well as magnetic transition at Tsm ~ 160K. The mode frequencies of two first-order Raman modes B1g and Eg, both involving displacement of Fe atoms, show sharp increase below Tsm. Concomitantly, the linewidths of all the first-order Raman modes show anomalous broadening below Tsm, attributed to strong spin-phonon coupling. The high frequency modes observed between 400-1200 cm-1 are attributed to the electronic Raman scattering involving the crystal field levels of d-orbitals of Fe2+. The splitting between xz and yz d-orbital levels is shown to be ~ 25 meV which increases as temperature decreases below Tsm. A broad Raman band observed at ~ 3200 cm-1 is assigned to two-magnon excitation of the itinerant Fe 3d antiferromagnet.