Electronic structure of the candidate 2D Dirac semimetal SrMnSb2: a combined experimental and theoretical study

TL;DR

This study combines experimental ARPES and theoretical calculations to analyze the electronic structure of SrMnSb2, revealing its trivial topology and 2D Dirac-like bands responsible for conductivity.

Contribution

It provides the first ARPES data on SrMnSb2 and demonstrates the non-topological nature of its electronic states through combined experimental and theoretical analysis.

Findings

SrMnSb2 has a small, 2D Fermi surface from linearly dispersing bands.

The ARPES data matches bulk-sensitive Shubnikov de Haas measurements.

Both theory and experiment show the Y-states are gapped and topologically trivial.

Abstract

SrMnSb$_2$ is suggested to be a magnetic topological semimetal. It contains square, 2D Sb planes with non-symmorphic crystal symmetries that could protect band crossings, offering the possibility of a quasi-2D, robust Dirac semi-metal in the form of a stable, bulk (3D) crystal. Here, we report a combined and comprehensive experimental and theoretical investigation of the electronic structure of SrMnSb$_2$, including the first ARPES data on this compound. SrMnSb$_2$ possesses a small Fermi surface originating from highly 2D, sharp and linearly dispersing bands (the Y-states) around the (0,$\pi$/a)-point in $k$-space. The ARPES Fermi surface agrees perfectly with that from bulk-sensitive Shubnikov de Haas data from the same crystals, proving the Y$-$states to be responsible for electrical conductivity in SrMnSb$_2$. DFT and tight binding (TB) methods are used to model the electronic states, and both show good agreement with the ARPES data. Despite the great promise of the latter, both theory approaches show the Y-states to be gapped above E$_F$, suggesting trivial topology. Subsequent analysis within both theory approaches shows the Berry phase to be zero, indicating the non-topological character of the transport in SrMnSb$_2$, a conclusion backed up by the analysis of the quantum oscillation data from our crystals.