Suppression of spin-exciton state in hole overdoped iron-based superconductors

TL;DR

This study investigates how magnetic excitations in hole overdoped iron-based superconductors change with doping, revealing a suppression of spin resonance signals and a shift of spectral weight to higher energies, indicating reduced magnetic influence on pairing.

Contribution

It provides the first detailed doping-dependent neutron scattering analysis showing suppression of spin resonance in overdoped regimes of Ba1-xKxFe2As2.

Findings

Spin resonance peaks are strong in optimally doped samples.

Resonance peaks are absent in overdoped samples.

Spectral weight shifts from below 2Ds to around 3Ds in overdoped samples.

Abstract

The mechanism of Cooper pair formation in iron-based superconductors remains a controversial topic. The main question is whether spin or orbital fluctuations are responsible for the pairing mechanism. To solve this problem, a crucial clue can be obtained by examining the remarkable enhancement of magnetic neutron scattering signals appearing in a superconducting phase. The enhancement is called spin resonance for a spin fluctuation model, in which their energy is restricted below twice the superconducting gap value (2Ds), whereas larger energies are possible in other models such as an orbital fluctuation model. Here we report the doping dependence of low-energy magnetic excitation spectra in Ba1-xKxFe2As2 for 0.5<x<0.84 studied by inelastic neutron scattering. We find that the behavior of the spin resonance dramatically changes from optimum to overdoped regions. Strong resonance peaks are observed clearly below 2Ds in the optimum doping region, while they are absent in the overdoped region. Instead, there is a transfer of spectral weight from energies below 2Ds to higher energies, peaking at values of 3Ds for x = 0.84. These results suggest a reduced impact of magnetism on Cooper pair formation in the overdoped region.