Possible pairing states of the Fe-based superconductors

TL;DR

This paper investigates possible pairing states in Fe-based superconductors using a two-band model, identifying sign-changing s-wave and double d-wave solutions, and analyzing their properties in relation to experimental data.

Contribution

It introduces a minimal two-band model with phenomenological interactions to explore and compare two distinct superconducting gap solutions in Fe-based superconductors.

Findings

Both gap solutions satisfy the relation Δ_h^max N_h ≈ Δ_e^max N_e.

Calculated properties include density of states, relaxation rate, Knight shift, and penetration depth.

Results align with experimental observations of Fe-based superconductors.

Abstract

We consider the minimal two-band model for the Fe-based superconductors with a phenomenological pairing interaction which mimics short-range antiferromagnetic (AFM) fluctuations. Two superconducting (SC) gap solutions are found to exist with the model: sign-changing s-wave gap ($\pm$s-wave) and double d-wave gap states. Both solutions hold the approximate relation $\Delta_{h} ^{max} N_h \approx \Delta_{e} ^{max} N_e$, a generic feature of two band model with a dominant interband pairing interaction. We carried out the calculations of the SC properties of the both SC states such as the density of states, temperature dependencies of spin-lattice relaxation rate $1/T_1$, Knight shift, and penetration depth, particularly taking into account of the interband coherence factors. The results are discussed in comparison with the currently available experimental data.