Nanomosaic of Topological Dirac States on the Surface of Pb₅Bi₂₄Se₄₁ Observed by Nano-ARPES

We have performed scanning angle-resolved photoemission spectroscopy with a nanometer-sized beam spot (nano-ARPES) on the cleaved surface of Pb₅Bi₂₄Se₄₁, which is a member of the (PbSe)₅(Bi₂Se₃)_3m homologous series (PSBS) with m = 4 consisting of alternate stacking of the topologically trivial insulator PbSe bilayer and four quintuple layers (QLs) of the topological insulator Bi₂Se₃. This allows us to visualize a mosaic of topological Dirac states at a nanometer scale coming from the variable thickness of the Bi₂Se₃ nanoislands (1-3 QLs) that remain on top of the PbSe layer after cleaving the PSBS crystal, because the local band structure of topological origin changes drastically with the thickness of the Bi₂Se₃ nanoislands. A comparison of the local band structure with that in ultrathin Bi₂Se₃ films on Si(111) gives us further insights into the nature of the observed topological states. This result demonstrates that nano-ARPES is a very useful tool for characterizing topological heterostructures.