A Generic Two-band Model for Unconventional Superconductivity and Spin-Density-Wave Order in Electron and Hole Doped Iron-Based Superconductors

TL;DR

This paper introduces a minimal two-band model for iron-based superconductors that captures both unconventional superconductivity and spin-density-wave order, explaining experimental observations and providing analytical relations for key parameters.

Contribution

It proposes a novel two-band Hamiltonian incorporating interband interactions, explaining SDW and superconductivity, and deriving formulas to determine model parameters from experiments.

Findings

The model reproduces a symmetric phase diagram for doping.

It predicts a nodal d-wave pairing symmetry.

Analytical relations help estimate band parameters from data.

Abstract

Based on experimental data on the newly synthesized iron-based superconductors and the relevant band structure calculations, we propose a minimal two-band BCS-type Hamiltonian with the interband Hubbard interaction included. We illustrate that this two-band model is able to capture the essential features of unconventional superconductivity and spin density wave (SDW) ordering in this family of materials. It is found that bound electron-hole pairs can be condensed to reveal the SDW ordering for zero and very small doping, while the superconducting ordering emerges at small finite doping, whose pairing symmetry is qualitatively analyzed to be of nodal d-wave. The derived analytical formulas not only give out a nearly symmetric phase diagram for electron and hole doping, but also is likely able to account for existing main experimental results. Moreover, we also derive two important relations for a general two-band model and elaborate how to apply them to determine the band width ratio and the effective interband coupling strength from experimental data.