Incommensurate spin fluctuations in hole-overdoped superconductor KFe2As2

TL;DR

This study reveals incommensurate low-energy spin fluctuations in heavily hole-overdoped KFe2As2, differing from electron-doped counterparts, and suggests these fluctuations are linked to superconductivity via interband scattering.

Contribution

It provides the first detailed neutron scattering analysis of spin fluctuations in heavily hole-doped KFe2As2, highlighting their incommensurate nature and origin from multiorbital band structure.

Findings

Incommensurate spin fluctuations at specific wave vectors.

Difference in peak splitting direction compared to electron-doped compounds.

Spin fluctuations are more robust in hole-doped samples.

Abstract

A neutron scattering study of heavily hole-overdoped superconducting KFe$_2$As$_2$ revealed a well-defined low-energy incommensurate spin fluctuation at [$\pi(1\pm2\delta$),0] with $\delta$ = 0.16. The incommensurate structure differs from the previously observed commensurate peaks in electron-doped $A$Fe$_2$As$_2$ ($A$ = Ba, Ca, or Sr) at low energies. The direction of the peak splitting is perpendicular to that observed in Fe(Te,Se) or in Ba(Fe,Co)$_2$As$_2$ at high energies. A band structure calculation suggests interband scattering between bands around the $\Gamma$ and X points as an origin of this incommensurate peak. The perpendicular direction of the peak splitting can be understood within the framework of multiorbital band structure. The results suggest that spin fluctuation is more robust in hole-doped than in electron-doped samples, which can be responsible for the appearance of superconductivity in the heavily hole-doped samples.