Density Functional Study of the Over-Doped Iron Chalcogenide: TlFe$_{2}$Se$_{2}$ with ThCr$_{2}$Si$_{2}$ structure

TL;DR

This study uses density functional theory to analyze the electronic and magnetic properties of TlFe$_{2}$Se$_{2}$, revealing its antiferromagnetic ground state, heavy electron doping, and similarities to Fe-based superconductors.

Contribution

First detailed density functional analysis of TlFe$_{2}$Se$_{2}$ in the ThCr$_{2}$Si$_{2}$ structure, highlighting its magnetic properties and electronic structure related to superconductivity.

Findings

Ground state is antiferromagnetic with checkerboard order.

Heavy electron doping due to Tl monovalency.

Fermi surface similar to Fe-based superconductors, with larger electron cylinders.

Abstract

We report density functional calculations of electronic structure and magnetic properties of ternary iron chalcogenide TlFe$_{2}$Se$_{2}$, which occurs in the ThCr$_{2}$Si$_{2}$ structure and discuss the results in relation to the iron-based superconductors. The ground state is antiferromagnetic with checkerboard order and Fe moment $\sim$ 1.90 $\mu$B. There is strong magnetoelastic coupling similar to the Fe-based superconductors, reflected in a sensitivity of the Se position to magnetism. Tl is monovalent in this compound, providing heavy electron-doping of 0.5 additional carriers per Fe relative to the parent compounds of the Fe-based superconductors. Other than the change in electron count, the electronic structure is rather similar to those materials. In particular, the Fermi surface is closely related to those of the Fe-based superconductors, except that the electron cylinders are larger, and the hole sections are suppressed. This removes the tendency towards a spin density wave.