Indirect evidence for strong coupling superconductivity in FeSe under pressure from first-principle calculations

TL;DR

This study uses first-principles calculations to analyze how pressure affects the electronic structure and superconductivity in FeSe, providing evidence that strong-coupling spin fluctuations are responsible for pairing rather than Fermi surface nesting.

Contribution

It demonstrates that Fermi surface nesting evolution does not explain Tc changes in FeSe under pressure, supporting a strong-coupling spin fluctuation pairing mechanism.

Findings

Fermi surface nesting does not correlate with Tc evolution in FeSe

Electronic band structures are highly sensitive to pressure application methods

Strong-coupling spin fluctuations likely drive superconductivity in FeSe

Abstract

Whether the pairing mechanism for superconductivity in iron-based superconductors is of itinerant or local character is a question still debated on. In order to investigate the influence of Fermi surface nesting, we calculate from first-principles the static susceptibility of FeSe under applied pressures, both hydrostatic and non-hydrostatic. We show that the electronic band structures are highly sensitive to the way pressure is applied and confront our theoretical results with conclusions drawn from experiments. Given that the critical temperature of FeSe is quite universal as function of pressure, this is clear evidence that in FeSe the evolution of Fermi surface nesting cannot account for the evolution of the critical temperature with pressure. Hence we argue that the pairing in iron-chalcogenide compounds should be of strong-coupling spin fluctuation origin.