Multigap superconductivity and strong electron-boson coupling in Fe-based superconductors: A point-contact Andreev-reflection study of Ba(Fe1-xCox)2As2 single crystals

TL;DR

This study uses point-contact Andreev-reflection measurements to reveal multigap superconductivity and strong electron-boson coupling in Ba(Fe1-xCox)2As2, aligning experimental data with a three-band Eliashberg model.

Contribution

It provides direct experimental evidence of two superconducting gaps and electron-boson interactions in Fe-based superconductors, modeled successfully with a three-band Eliashberg approach.

Findings

Identification of two superconducting gaps without line nodes.

Observation of electron-boson interaction features matching neutron scattering data.

Reproduction of spectra using a three-band s+- Eliashberg model.

Abstract

Directional point-contact Andreev-reflection (PCAR) measurements in Ba(Fe1-xCox)2As2 single crystals (Tc=24.5 K) indicate the presence of two superconducting gaps with no line nodes on the Fermi surface. The PCAR spectra also feature additional structures related to the electron-boson interaction, from which the characteristic boson energy Omega_b(T) is obtained, very similar to the spin-resonance energy observed in neutron scattering experiments. Both the gaps and the additional structures can be reproduced within a three-band s+- Eliashberg model by using an electron-boson spectral function peaked at Omega_0 = 12 meV ~ Omega_b(0).