AFeSe2 (A=Tl, K, Rb, or Cs): Iron-based superconducting analog of the cuprates

TL;DR

This study predicts that AFeSe2 compounds share key structural and electronic features with cuprate superconductors, including antiferromagnetic insulating states and strong exchange interactions, suggesting potential for high-temperature superconductivity upon doping.

Contribution

First-principles calculations reveal AFeSe2 compounds as cuprate analogs with similar structures, magnetic properties, and potential for superconductivity upon doping.

Findings

AFeSe2 has a layered structure similar to cuprates.

They are antiferromagnetic insulators with small charge gaps.

Exchange interactions are comparable to cuprates.

Abstract

It has long been a challenging task to find compounds with similar crystal and electronic structures as cuprate superconductors with low dimensionality and strong antiferromagnetic fluctuations. The parent compounds of cuprate superconductors are Mott insulators with strong in-plane antiferromagnetic exchange interactions between Cu moments. Here we show, based on first-principles density functional calculations, that AFeSe2 (A=Tl, K, Rb, or Cs) exhibit many of the physical properties common to the cuprate parent compounds: (1) the FeSe2 layer in AFeSe2 is similar in crystalline and electronic structures to the CuO2 plane in cuprates, although Se atoms are not coplanar to the square Fe-lattice; (2) they are antiferromagnetic insulators, but with relatively small charge excitation gaps; (3) their ground states are Neel antiferromagnetic ordered, similar as in cuprates; and (4) the antiferromagnetic exchange interactions between Fe moments are larger than in other iron-based superconducting materials, but comparable to those in cuprates. Like cuprates, these compounds may become high-Tc superconductors upon doping of charge carriers either by chemical substitution or intercalation or by liquid or solid gating.