Phase diagram and a possible unified description of intercalated iron selenide superconductors

TL;DR

This paper presents a theoretical phase diagram for intercalated iron selenide superconductors, highlighting the coexistence of local moments and itinerant electrons, and describes their superconducting and insulating states.

Contribution

It introduces a unified theoretical framework for understanding the phase diagram and properties of A2Fe4Se5-type superconductors based on combined local moment and itinerant electron models.

Findings

Superconducting s-wave pairing at M pockets identified

Insulating state at low doping and CDW at high doping characterized

Consistency with experimental susceptibility and resistivity data achieved

Abstract

We propose a theoretical description of the phase diagram and physical properties in A2Fe4Se5-type (A=K, Tl) compounds based on a coexistent local moment and itinerant electron picture. Using neutron scattering and ARPES measurements to fix the general structure of the local moment and itinerant Fermi pockets, we find a superconducting (SC) regime with s-wave pairing at the M pockets and an incipient sign-change s-wave near the Gamma point, which is adjacent to an insulating state at low doping and a charge-density-wave (CDW) state at high doping. The uniform susceptibility and resistivity are found to be consistent with the experiment. The main distinction with iron pnictide superconductors is also discussed.