# Momentum Dependence of the Nematic Order Parameter in Iron-Based Superconductors

## TL;DR

This study investigates the momentum dependence of the nematic order parameter in iron-based superconductors, revealing a consistent sign change between different momentum points in FeSe and BaFe₂As₂, suggesting a common underlying mechanism.

## Contribution

It provides the first direct measurement of the nematic order parameter’s momentum dependence in multiple compounds using ARPES with strain tuning.

## Key findings

- Nematic order parameter changes sign between Brillouin center and corner.
- Same momentum dependence observed in FeSe and BaFe₂As₂.
- Indicates a common microscopic mechanism for nematic order.

## Abstract

The momentum dependence of the nematic order parameter is an important ingredient in the microscopic description of iron-based high-temperature superconductors. While recent reports on FeSe indicate that the nematic order parameter changes sign between electron and hole bands, detailed knowledge is still missing for other compounds. Combining angle-resolved photoemission spectroscopy (ARPES) with uniaxial strain tuning, we measure the nematic band splitting in both FeSe and BaFe$_2$As$_2$ without interference from either twinning or magnetic order. We find that the nematic order parameter exhibits the same momentum dependence in both compounds with a sign change between the Brillouin center and the corner. This suggests that the same microscopic mechanism drives the nematic order in spite of the very different phase diagrams.