  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.
