Angle-resolved photoemission studies of the superconducting gap symmetry in Fe-based superconductors

TL;DR

This paper uses angle-resolved photoemission spectroscopy to analyze the superconducting gap symmetry in Fe-based superconductors, revealing a Fermi surface dependent, nodeless gap with small anisotropy, supporting strong coupling models.

Contribution

It provides experimental evidence for the momentum-dependent, nodeless superconducting gap in Fe-based superconductors, challenging weak coupling theories and highlighting the role of interband scattering.

Findings

Superconducting gap is Fermi surface dependent and nodeless.

Strong coupling models better explain the observed gap symmetry.

Anisotropies are due to Cooper pair lifetime, not pairing mechanism.

Abstract

The superconducting gap is the fundamental parameter that characterizes the superconducting state, and its symmetry is a direct consequence of the mechanism responsible for Cooper pairing. Here we discuss about angle-resolved photoemission spectroscopy measurements of the superconducting gap in the Fe-based high-temperature superconductors. We show that the superconducting gap is Fermi surface dependent and nodeless with small anisotropy, or more precisely, a function of momentum. We show that while this observation is inconsistent with weak coupling approaches for superconductivity in these materials, it is well supported by strong coupling models and global superconducting gaps. We also suggest that the strong anisotropies measured by other probes sensitive to the residual density of states are not related to the pairing interaction itself, but rather emerge naturally from the smaller lifetime of the superconducting Cooper pairs that is a direct consequence of the momentum dependent interband scattering inherent to these materials.