Interplay of lattice, electronic and spin degrees of freedom in detwinned BaFe$_{2}$As$_{2}$: a Raman scattering study

TL;DR

This study uses Raman scattering to explore how electronic, spin, and lattice interactions influence phonon behavior in detwinned BaFe$_{2}$As$_{2}$, revealing orbital-selective correlations and magnetic effects on lattice dynamics.

Contribution

It provides new insights into the interplay of electronic, magnetic, and lattice degrees of freedom in BaFe$_{2}$As$_{2}$ through combined experimental and theoretical analysis.

Findings

$E_g$ modes split in the orthorhombic phase

Spectral weight of As mode varies with laser energy and polarization

Magnetic ordering significantly affects phonon anomalies

Abstract

We report results of Raman scattering experiments on twin-free BaFe$_{2}$As$_{2}$ with the main focus placed on understanding the influence of electronic and spin degrees of freedom on the lattice dynamics. In particular, we scrutinize the $E_g$ modes and the As $A_{1g}$ mode. Each of the two $E_g$ phonons in the tetragonal phase is observed to split into a $B_{2g}$ and a $B_{3g}$ mode upon entering the orthorhombic stripe-magnetic phase. The splitting amounts to approximately 10\,cm$^{-1}$ and less than 5\,cm$^{-1}$ for the low- and the high-energy $E_g$ mode, respectively. The detailed study of the fully symmetric As mode using parallel incident and outgoing photon polarizations along either the antiferromagnetic or the ferromagnetic Fe-Fe direction reveals an anisotropic variation of the spectral weight with the energy of the exciting laser indicating a polarization-dependent resonance effect. Along with the experiments we present results from density functional theory calculations of the phonon eigenvectors, the dielectric function, and the Raman tensor elements. The comparison of theory and experiment indicates that (i) orbital-selective electronic correlations are crucial to understand the lattice dynamics and (ii) all phonon anomalies originate predominantly from the magnetic ordering and the corresponding reconstruction of the electronic bands at all energies.