Evidence of a spin resonance mode in the iron-based superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ from scanning tunneling spectroscopy

TL;DR

This study uses scanning tunneling spectroscopy to identify a spin resonance mode in the iron-based superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$, revealing strong electron-spin coupling linked to superconductivity.

Contribution

First direct observation of a spin resonance mode in Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ using tunneling spectroscopy, connecting spin excitations with superconductivity in iron pnictides.

Findings

Detection of a bosonic mode at ~14 meV in the density of states.

Mode energy closely matches neutron scattering spin resonance.

Evidence of strong electron-spin excitation coupling in the material.

Abstract

We used high-resolution scanning tunneling spectroscopy to study the hole-doped iron pnictide superconductor Ba$_{0.6}$K$_{0.4}$Fe$_{2}$As$_{2}$ ($T_c=38$ K). Features of a bosonic excitation (mode) are observed in the measured quasiparticle density of states. The bosonic features are intimately associated with the superconducting order parameter and have a mode energy of $\sim$14 meV, similar to the spin resonance measured by inelastic neutron scattering. These results indicate a strong electron-spin excitation coupling in iron pictnide superconductors, similar to that in high-$T_c$ copper oxide superconductors.