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

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 $A{\\mathrm{FeSe}}_{2}$ ($A=\\text{Tl}$, K, Rb, or Cs) exhibit many of the physical properties common to the cuprate parent compounds: (1) The ${\\mathrm{FeSe}}_{2}$ layer in $A{\\mathrm{FeSe}}_{2}$ is similar in crystalline and electronic structures to the ${\\mathrm{CuO}}_{2}$ 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 N\\\u0027eel 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. As cuprates, these compounds may become high-${T}_{c}$ superconductors upon doping of charge carriers either by chemical substitution or intercalation or by liquid or solid gating.