# Superconductivity in Uncollapsed Tetragonal LaFe2As2

## TL;DR

This study demonstrates that uncollapsed tetragonal LaFe2As2 exhibits superconductivity at 12.1 K after annealing, with structural changes affecting its electronic properties and potential pairing mechanisms.

## Contribution

It reveals the emergence of superconductivity in LaFe2As2 through structural transition from collapsed to uncollapsed tetragonal phase.

## Key findings

- Superconductivity appears at 12.1 K in uncollapsed tetragonal La122.
- Annealing induces a structural transition from collapsed to uncollapsed tetragonal.
- The Fermi surface changes due to electron doping, affecting pairing mechanisms.

## Abstract

We report synthesis, crystal structure and superconductivity in ThCr2Si2-type LaFe2As2 (La122). La122 was synthesized at 960{\deg}C for 1.5 h under a pressure of 3.4 GPa. An as-synthesized La122 (non-superconductor) had a collapsed tetragonal structure with a short c-axis length of 11.0144(4) {\AA} as observed in CaFe2As2 under pressure. The collapsed tetragonal transformed into an uncollapsed tetragonal by annealing the as-synthesized La122 at 500{\deg}C. The c-axis length remarkably extended to 11.7317(4) {\AA} and superconductivity emerged at 12.1 K in the uncollapsed tetragonal La122. A cylindrical hole-like Fermi-surface around the {\Gamma} point that plays an important role for an s+-wave paring in iron-based superconductors was missing in the uncollapsed tetragonal La122 due to heavily electron-doping. Superconductivity in La122 may be closely related to that induced in CaFe2As2 under pressure.

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Source: https://tomesphere.com/paper/1905.06524