Phonon splitting and anomalous enhancement of infrared-active modes in BaFe$_2$As$_2$

TL;DR

This study investigates lattice vibrations in BaFe₂As₂, revealing phonon mode splitting and strength enhancement linked to structural transition and anisotropic conductivity caused by Hund's coupling.

Contribution

It provides detailed infrared spectroscopic data on phonon behavior across phase transition and explains anomalous phonon enhancement through anisotropic conductivity mechanisms.

Findings

Observation of phonon mode splitting after structural transition

Significant phonon strength enhancement in orthorhombic phase

Explanation of enhancement via anisotropic conductivity and Hund's coupling

Abstract

We present a comprehensive infrared spectroscopic study of lattice dynamics in the pnictide parent compound BaFe$_2$As$_2$. In the tetragonal structural phase, we observe the two degenerate symmetry-allowed in-plane infrared active phonon modes. Following the structural transition from the tetragonal to orthorhombic phase, we observe splitting into four non-degenerate phonon modes and a significant phonon strength enhancement. These detailed data allow us to provide a physical explanation for the anomalous phonon strength enhancement as the result of anisotropic conductivity due to Hund's coupling.