Electronic Structure, Topological Phase Transitions and Superconductivity in (K,Cs)xFe2Se2

TL;DR

This paper investigates the electronic structures and topological phase transitions in hole-doped KxFe2Se2 and CsxFe2Se2 superconductors, revealing how their Fermi surfaces evolve with doping and relate to superconducting properties.

Contribution

It provides a detailed comparison of the electronic structures of KxFe2Se2 and CsxFe2Se2 with BaFe2As2, highlighting topological Fermi surface transitions and their correlation with superconductivity.

Findings

Fermi surfaces of KxFe2Se2 and CsxFe2Se2 resemble BaFe2As2 at 60% hole doping.

Topological Fermi surface transitions occur near the G point with doping.

Superconducting Tc correlates with the density of states at the Fermi level.

Abstract

We present LDA band structure of novel hole doped high temperature superconductors (Tc~30K) KxFe2Se2 and CsxFe2Se2 and compare it with previously studied electronic structure of isostructural FeAs superconductor BaFe2As2 (Ba122). We show that stoichiometric KFe2Se2 and CsFe2Se2 have rather different Fermi surfaces as compared with Ba122. However at about 60% of hole doping Fermi surfaces of novel materials closely resemble those of Ba122. In between these dopings we observe a number of topological Fermi surface transitions near the G point in the Brillouin zone. Superconducting transition temperature Tc of new systems is apparently governed by the value of the total density of states (DOS) at the Fermi level.