Band inversion and topology of the bulk electronic structure in FeSe${}_{0.45}$Te${}_{0.55}$

TL;DR

This study uses ARPES to demonstrate band inversion in FeSe${}_{0.45}$Te${}_{0.55}$, providing direct evidence of a topologically non-trivial bulk electronic structure that supports surface states relevant for topological superconductivity.

Contribution

First direct ARPES evidence of bulk band inversion in FeSe${}_{0.45}$Te${}_{0.55}$, confirming its topologically non-trivial nature and potential for hosting Majorana states.

Findings

Periodic variation of ARPES intensity with $k_z$ indicates band inversion.

No significant $k_z$ dispersion of the valence band top.

Evidence of parity change from $ ext{Γ}$ to Z points.

Abstract

FeSe${}_{0.45}$Te${}_{0.55}$ (FeSeTe) has recently emerged as a promising candidate to host topological superconductivity, with a Dirac surface state and signatures of Majorana bound states in vortex cores. However, correlations strongly renormalize the bands compared to electronic structure calculations, and there is no evidence for the expected bulk band inversion. We present here a comprehensive angle resolved photoemission (ARPES) study of FeSeTe as function of photon energies ranging from 15 - 100 eV. We find that although the top of bulk valence band shows essentially no $k_z$ dispersion, its normalized intensity exhibits a periodic variation with $k_z$. We show, using ARPES selection rules, that the intensity oscillation is a signature of band inversion indicating a change in the parity going from $\Gamma$ to Z. Thus we provide the first direct evidence for a topologically non-trivial bulk band structure that supports protected surface states.