Nematic Pairing from Orbital Selective Spin Fluctuations in FeSe

TL;DR

This paper proposes that orbital-selective spin fluctuations drive nematic pairing in FeSe, explaining its anisotropic superconducting gaps and nematic state without magnetism, with implications for understanding its superconducting properties.

Contribution

It introduces a spin-nematic scenario based on orbital-selective spin fluctuations that accounts for nematicity and gap anisotropy in FeSe.

Findings

Orbital-selective spin fluctuations mediate nematic pairing.

Anisotropic spin modes lead to orbital and nematic selectivity.

The model predicts a $k_z$ dependence of the gap anisotropy.

Abstract

FeSe is an intriguing iron-based superconductor. It presents an unusual nematic state without magnetism and can be tuned to increase the critical superconducting temperature. Recently it has been observed a noteworthy anisotropy of the superconducting gaps. Its explanation is intimately related to the understanding of the nematic transition itself. Here we show that the spin-nematic scenario driven by orbital-selective spin-fluctuations provides a simple scheme to understand both phenomena. The pairing mediated by anisotropic spin modes is not only orbital selective but also nematic, leading to stronger pair scattering across the hole and $X$ electron pocket. The delicate balance between orbital ordering and nematic pairing points also to a marked $k_z$ dependence of the hole-gap anisotropy.