Effect of K Doping on Phonons in Ba1-xKxFe2As2

TL;DR

This study investigates how potassium doping affects phonon behavior in Ba1-xKxFe2As2, revealing phonon softening, broadening, and new modes due to local distortions and possible electron-phonon interactions.

Contribution

It provides detailed experimental and theoretical analysis of phonon modifications caused by K doping in Ba1-xKxFe2As2, highlighting the mechanisms behind phonon softening and mode emergence.

Findings

K doping causes phonon softening and broadening in Ba1-xKxFe2As2.

New phonon modes appear at specific wave vectors in doped samples.

Local distortions and electron-phonon coupling are linked to observed phonon changes.

Abstract

The lattice dynamics of Ba1-xKxFe2As2 (x = 0.00, 0.27) have been studied by inelastic X-ray scattering measurement at room temperature. K doping induces the softening and broadening of phonon modes in the energy range E = 10-15 meV. Analysis with a Born-von Karman force-constant model indicates that the softening results from reduced interatomic force constants around (Ba,K) sites following the displacement of divalent Ba by monovalent K. The phonon broadening may be explained by the local distortions induced by the K substitution. Extra phonon modes are observed around the wave vector q = (0.5,0,0) at E = 16.5 meV for the x = 0.27 sample. These modes may arise either from the local disorder induced by K doping or from electron-phonon coupling.