Comparison of Tunneling in Fe-based Superconductors with Multi-band MgB$_{\mathrm{2}}$

MgB$_{\mathrm{2}}$ is an s-wave, phonon coupled, multiband superconductor that exhibits novel tunneling spectra including a subtle dip feature due to quasiparticle transfer between bands. Since this feature mimics the above-gap spectral dip feature observed in Fe-based superconductors, typically attributed to a strong coupling boson, it is worthwhile to consider whether quasiparticle transfer is relevant. We first show that the dip in MgB$_{\mathrm{2}}$ appears in the $\pi $-band, DOS ($\Delta =$2.4 meV) and is due to quasiparticle transfer to the $\sigma $-band with $\Delta =$7.2 meV. Reviewing the spectral dip in Fe-based superconductors, including new data on FeSe crystals, there are inconsistencies with quasiparticle transfer as the origin. The conclusion is that the spectral dip is more likely due to a boson, the resonance spin excitation, as found in cuprate superconductors.