# Novel Fe-based superconductor LaFe2As2 in comparison with traditional pnictides

## TL;DR

LaFe2As2, a novel Fe-based superconductor with unusual doping and Fermi surface features, challenges previous understanding and shows similarities to traditional FeBS physics despite its distinct properties.

## Contribution

This study reveals that LaFe2As2, despite its atypical doping and Fermiology, shares key magnetic and electronic characteristics with conventional FeBS superconductors.

## Key findings

- Superconducts at 12.1 K despite high apparent doping
- Two phases with magnetic origin identified
- Effective doping reduced to 0.30-0.35e due to valence state

## Abstract

The recently discovered Fe-based superconductor (FeBS) LaFe2As2 seems to break away from an established pattern that doping FeBS beyond 0.2e/Fe destroys superconductivity. LaFe2As2 has an apparent doping of 0.5e, yet superconducts at 12.1 K. Its Fermi surface bears no visual resemblance with the canonical FeBS Fermiology. It also exhibits two phases, none magnetic and only one superconducting. We show that the difference between them has nonetheless magnetic origin, the one featuring disordered moments, and the other locally nonmagnetic. We find that La there assumes an unusual valence of +2.6 to +2.7, so that the effective doping is reduced to 0.30-0.35e. A closer look reveals the same key elements: hole Fermi surfaces near Gamma-Z and electron ones near the X-P lines, with the corresponding peak in susceptibility, and a strong tendency to stripe magnetism. The physics of LaFe2As2 is thus more similar to the FeBS paradigm than hitherto appreciated.