Spin-phonon coupling and pressure effect in the superconductor LiFeAs : Lattice dynamics from first-principles calculations

TL;DR

This study uses first-principles calculations to explore how pressure and magnetic phases affect lattice dynamics and electron-phonon interactions in LiFeAs, revealing spin-phonon coupling influences and pressure effects on superconductivity.

Contribution

It provides detailed insights into the pressure dependence and magnetic phase effects on phonon behavior and electron-phonon coupling in LiFeAs, highlighting the role of spin-phonon interactions.

Findings

Phonon softening in SAF phase enhances electron-phonon coupling.

Anisotropic phonon softening arises from spin order differences.

Pressure influences electronic states and phonon frequencies, explaining Tc behavior.

Abstract

The lattice dynamics and the effect of pressure on superconducting LiFeAs in both nonmagnetic (NM) and striped antiferromagnetic (SAF) phases are investigated using the plane-wave pseudopotential, density-functional-based method. While the obtained electron-phonon coupling $\lambda$ is very small for the NM calculation, the softening of phonon in the SAF phase may lead to a large increase in $\lambda$. In the SAF phase, strong anisotropy of the phonon softening in the Fe plane is found to arise from different spin orders in the $x$ and $y$ directions, indicating that the phonon softening is of spin-phonon coupling origin. For the SAF structure, the calculated variation trend of the electronic density of states and the phonon frequencies under pressure can explain a large negative pressure coefficient of $T_{c}$ in the LiFeAs compound.