Strong local moment antiferromagnetic spin fluctuations in V-doped LiFeAs

TL;DR

This study investigates how vanadium doping affects the magnetic excitations and superconductivity in LiFeAs, revealing enhanced magnetic moments and suppressed superconductivity, supported by theoretical calculations.

Contribution

It provides new insights into the effects of vanadium doping on magnetic properties and superconductivity in LiFeAs, highlighting a possible spin crossover ground state.

Findings

Vanadium doping enhances magnetic scattering in LiFeAs.

Superconductivity is suppressed upon V-doping.

Magnetic excitations become longitudinally elongated with doping.

Abstract

We use neutron scattering to study vanadium (hole)-doped LiFe$_{1-x}$V$_x$As. In the undoped state, LiFeAs exhibits superconductivity at $T_c=18$ K and transverse incommensurate spin excitations similar to electron overdoped iron pnictides. Upon vanadium-doping to form LiFe$_{0.955}$V$_{0.045}$, the transverse incommensurate spin excitations in LiFeAs transform into longitudinally elongated in a similar fashion as that of potassium (hole) doped Ba$_{0.7}$K$_{0.3}$Fe$_2$As$_2$, but with dramatically enhanced magnetic scattering and elimination of superconductivity. This is different from the suppression of the overall magnetic excitations in hole doped BaFe$_2$As$_2$ and the enhancement of superconductivity near optimal hole doping. These results are consistent with density function theory plus dynamic mean field theory calculations, suggesting that vanadium-doping in LiFeAs may induce an enlarged effective magnetic moment $S_{eff}$ with a spin crossover ground state arising from the inter-orbital scattering of itinerant electrons.