Observation of an electron band above the Fermi level in FeTe$_{0.55}$Se$_{0.45}$ from \emph{in-situ} surface doping

TL;DR

This study demonstrates how in-situ potassium surface doping can tune the electronic structure of FeTe$_{0.55}$Se$_{0.45}$, revealing an electron band above the Fermi level and providing insights into unoccupied states in iron-based superconductors.

Contribution

We show that in-situ surface doping enables access to unoccupied electronic states in FeTe$_{0.55}$Se$_{0.45}$, revealing an electron band above the Fermi level.

Findings

Electrons are doped into the system via potassium evaporation.

An electron band above the Fermi level is observed.

The electron band resembles a small 3D pocket in KFe$_{2-x}$Se$_2$.

Abstract

We used \emph{in-situ} potassium (K) evaporation to dope the surface of the iron-based superconductor FeTe$_{0.55}$Se$_{0.45}$. The systematic study of the bands near the Fermi level confirms that electrons are doped into the system, allowing us to tune the Fermi level of this material and to access otherwise unoccupied electronic states. In particular, we observe an electron band located above the Fermi level before doping that shares similarities with a small three-dimensional pocket observed in the cousin, heavily-electron-doped KFe$_{2-x}$Se$_2$ compound.