Scaling of the superconducting gap with orbital character in FeSe

It is often hypothesized that superconductivity in the iron-based superconductors is mediated by a spin-fluctuation pairing mechanism, however direct evidence of this pairing is challenging to obtain. Here we present a high-resolution angle-resolved photoemission spectroscopy (ARPES) study on the three-dimensional superconducting gap of FeSe. We observe a direct scaling between the d_yz orbital weight at the Fermi level and the size of the superconducting gap at both the hole and electron pockets. Suggesting that superconducting pairing is mediated by strong, local Coulomb interactions.

We then present an ARPES-derived tight binding model which quantitatively takes into account all the features present in the nematic phase of FeSe; including spin-orbital coupling, nematic ordering, and most crucially the incoherence of an electron pocket. Using this model, we show that the calculated momentum dependence of the superconducting gap, assuming spin-fluctuation mediated superconductivity, directly reproduces the experimental results.

These findings provide both experimental and theoretical support for spin-fluctuation mediated superconductivity in FeSe.

L.C. Rhodes et. al. (2018) arXiv:1804.01436