Whether it is possible to stabilize the 1144-phase pnictides with tri-valence cations?

TL;DR

This study investigates the stability of 1144-phase pnictides with tri-valence cations and transition metal substitutions using density functional theory, identifying specific stable compounds and their electronic properties relevant to superconductivity.

Contribution

It proposes new stable 1144-phase pnictides with tri-valence cations and cobalt substitution, expanding the understanding of their electronic structures and potential superconductivity.

Findings

LaKFe4As4, LaRbFe4As4, LaCsFe4As4 are stable with semi-metal features.

InCo2As2 and TlCo2As2 are stabilized as cobalt arsenides.

Certain compounds with La, In, Tl show promising Fermi surface topology for superconductivity.

Abstract

The 1144 iron arsenide (e.g. CaKFe4As4) has recently been discovered and inspired a tide of search for superconductors. Such far, the discovered compounds are confined to iron arsenides (ABFe4As4), where A and B are either alkali metals or alkaline earth elements. In this work, we propose two directions in searching 1144 structures: (i) using tri-valence cations for A; (ii) substituting the transition metal, e.g. replacing Fe by Co. Following the two directions, we employ density functional theory to study stability and electronic structures of 1144 pnictides of various tri-valence cations (La, Y, In, Tl, Sm and Gd), as well as cobalt arsenides. For LaAFe4As4, the 1144 phase can be stabilized in three systems: LaKFe4As4, LaRbFe4As4 and LaCsFe4As4, which show quasi-two-dimensional semi-metal features similar to the iron pnictide superconductors: hole-type Fermi surface at Gama point and electron-type Fermi surface at M point in B.Z. In addition, LaKFe4As4 feature an extra bubble shaped Fermi surface sheets, distinct from the other two peers. Y does not support any 1144 phase within our search. For In and Tl, substitute Fe by Co and two unknown compounds of the 122 phase are stabilized: InCo2As2 and TlCo2As2. The two cobalt arsenides have Fermi surfaces of similar topology as iron arsenides, but the Fermi surfaces are all electron-type, showing potentials to be undiscovered superconductors. Stable 1144 phases are also found in InKCo4As4 and InRbCo4As4. For Sm and Gd, most 1144 and 122 iron arsenides are found unstable.