Common ($\pi$,$\pi$) Band Folding and Surface Reconstruction in FeAs-Based Superconductors

TL;DR

This study uses ARPES and STM to reveal common ($$,$$) band folding and surface reconstruction in FeAs-based superconductors, offering new insights into their electronic structure and superconductivity mechanisms.

Contribution

It demonstrates that ($$,$$) band folding and $$,$$) surface reconstruction are universal features in FeAs superconductors, linking surface phenomena to bulk electronic properties.

Findings

Observation of ($$,$$) band folding in all studied compounds.

Detection of $$,$$) surface reconstruction on CaKFe$_4$As$_4$.

Proposed that surface reconstruction explains the origin of band folding.

Abstract

High resolution angle-resolved photoemission spectroscopy (ARPES) measurements are carried out on CaKFe$_4$As$_4$, KCa$_2$Fe$_4$As$_4$F$_2$ and (Ba$_{0.6}$K$_{0.4}$)Fe$_2$As$_2$ superconductors. Clear evidence of band folding between the Brillouin zone center and corners with a ($\pi$,$\pi$) wave vector has been found from the measured Fermi surface and band structures in all the three kinds of superconductors. A dominant $\sqrt{2}\,\times\,\sqrt{2}$ surface reconstruction is observed on the cleaved surface of CaKFe$_4$As$_4$ by scanning tunneling microscopy (STM) measurements. We propose that the commonly observed $\sqrt{2}\,\times\,\sqrt{2}$ reconstruction in the FeAs-based superconductors provides a general scenario to understand the origin of the ($\pi$,$\pi$) band folding. Our observations provide new insights in understanding the electronic structure and superconductivity mechanism in iron-based superconductors.