Spin-Peierls-like transition in AFe$_2$As$_2$(A=Ba, Sr)

TL;DR

This study combines first-principles calculations and Raman experiments to reveal a spin-Peierls-like transition in AFe₂As₂ compounds, driven by phonon-spin coupling, explaining their magnetic and structural phase changes.

Contribution

It demonstrates that phonon-spin coupling causes the structural transition in AFe₂As₂, a novel insight into the mechanism of phase transitions in these materials.

Findings

Identification of a spin-Peierls-like transition at low temperature.

Phonon-spin coupling as the main driver of structural change.

Explanation of magnetic and structural phase transitions observed experimentally.

Abstract

From first-principles density functional theory calculations combined with varying temperature Raman experiments, we show that AFe$_2$As$_2$ (A=Ba, Sr), the parent compound of the FeAs based superconductors of the new structural family, undergoes a spin-Peierls-like phase transition at low temperature. The coupling between the phonons and frustrated spins is proved to be the main cause of the structural transition from the tetragonal to orthorhombic phase. These results well explain the magnetic and structural phase transitions in AFe$_2$As$_2$(A=Ba, Sr) recently observed by neutron scattering.