Predicted electronic markers for polytypes of LaOBiS2 examined via angular resolved photoemission spectroscopy

TL;DR

This study demonstrates how electronic markers derived from ARPES can distinguish between nearly energetically degenerate polytypes of LaOBiS2, revealing subtle structural differences through their unique Rashba-related electronic features.

Contribution

The paper introduces a method to identify polytypes of LaOBiS2 using ARPES-detected electronic markers linked to Rashba physics, supported by DFT calculations.

Findings

Distinct electronic markers for different polytypes identified

ARPEs measurements confirmed the dominant polytype in samples

Electronic markers can differentiate nearly degenerate structural variants

Abstract

The natural periodic stacking of symmetry-inequivalent planes in layered compounds can lead to the formation of natural superlattices; albeit close in total energy, (thus in their thermodynamic stability), such polytype superlattices can exhibit different structural symmetries, thus have markedly different electronic properties which can in turn be used as "structural markers". We illustrate this general principle on the layered LaOBiS2 compound where density-functional theory (DFT) calculations on the (BiS2)/(LaO)/(BiS2) polytype superlattices reveal both qualitatively and quantitatively distinct electronic structure markers associated with the Rashba physics, yet the total energies are only ~ 0.1 meV apart. This opens the exciting possibility of identifying subtle structural features via electronic markers. We show that the pattern of removal of band degeneracies in different polytypes by the different forms of symmetry breaking leads to new Rashba "mini gaps" with characteristic Rashba parameters that can be determined from spectroscopy, thereby narrowing down the physically possible polytypes. By identifying these distinct DFT-predicted fingerprints via ARPES measurements on LaBiOS2 we found the dominant polytype with small amounts of mixtures of other polytypes. This conclusion, consistent with neutron scattering results, establishes ARPES detection of theoretically established electronic markers as a powerful tool to delineate energetically quasidegenerate polytypes.