Coherence effect in a two-band superconductor: Application to iron pnictides

TL;DR

This paper proposes an experimental approach to distinguish pairing symmetries in iron pnictides by analyzing temperature-dependent response functions at the nesting vector, highlighting the coherence effect in two-band superconductors.

Contribution

It introduces a method to identify pairing symmetry in iron pnictides using response function measurements, emphasizing the coherence effect's role in differentiating $s_{+-}$ and $s_{++}$ states.

Findings

Distinct temperature dependence of response functions for $s_{+-}$ and $s_{++}$ states.

The coherence effect causes observable differences in neutron scattering measurements.

Proposes neutron scattering as a tool to determine pairing symmetry.

Abstract

From a theoretical point of view, we propose an experimental method to determine the pairing symmetry of iron pnictides. We focus on two kinds of pairing symmetries, $s_{+-}$ and $s_{++}$, which are strong candidates for the pairing symmetry of iron pnictides. For each of these two symmetries, we calculate both the density and spin response functions by using the two-band BCS model within the one-loop approximation. As a result, a clear difference is found between the $s_{+-}$- and $s_{++}$-wave states in the temperature dependence of the response functions at nesting vector $\bf{Q}$, which connects the hole and electron Fermi surfaces. We point out that this difference comes from the coherence effect in the two-band superconductor. We suggest that the pairing symmetry could be clarified by observing the temperature dependence of both the density and spin structure factors at the nesting vector $\bf{Q}$ in neutron scattering measurements.