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 Rashba “minigaps” 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 angle-resolved photoemission spectroscopy (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.
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This paper was funded by National Science Foundation (NSF) Designing Materials to Revolutionize and Engineer our Future (DMREF) Project No. DMR-1334170 to the University of Colorado and the University of Kentucky. The Advanced Light Source is supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.
Zhou, Xiaoqing; Liu, Qihang; Waugh, J. A.; Nummy, T.; Zhang, Xiuwen; Zhu, Xiangde; Cao, Gang; Zunger, Alex; and Dessau, D. S., "Predicted Electronic Markers for Polytypes of LaOBiS2 Examined via Angle-Resolved Photoemission Spectroscopy" (2017). Physics and Astronomy Faculty Publications. 521.