One-Fe versus Two-Fe Brillouin Zone of Fe-Based Superconductors: Creation of the Electron Pockets via Translational Symmetry Breaking

TL;DR

This paper explores how translational symmetry breaking in Fe-based superconductors affects their electronic structure, revealing the creation of electron pockets only when symmetry breaking is considered, which impacts understanding of their superconducting properties.

Contribution

It demonstrates that considering translational symmetry breaking is essential for accurately modeling the electronic structure and electron pockets in Fe-based superconductors.

Findings

Unfolded band structures show orbital character changes across the one-Fe Brillouin zone.

Electron pockets are only formed when symmetry breaking is included.

Full inclusion of symmetry breaking is crucial for understanding superconducting properties.

Abstract

We investigate the physical effects of translational symmetry breaking in Fe-based high-temperature superconductors due to alternating anion positions. In the representative parent compounds, including the newly discovered Fe-vacancy-ordered $\mathrm{K_{0.8}Fe_{1.6}Se_2}$, an unusual change of orbital character is found across the one-Fe Brillouin zone upon unfolding the first-principles band structure and Fermi surfaces, suggesting that covering a larger one-Fe Brillouin zone is necessary in experiments. Most significantly, the electron pockets (critical to the magnetism and superconductivity) are found only created with the broken symmetry, advocating strongly its full inclusion in future studies, particularly on the debated nodal structures of the superconducting order parameter.