Emergent and Tunable Topological Surface States in Complementary Sb/Bi₂Te₃ and Bi₂Te₃/Sb Thin-Film Heterostructures

Epitaxial thin-film heterostructures offer a versatile platform for realizing topological surface states (TSSs) that may be emergent and/or tunable by tailoring the atomic layering in the heterostructures. Here, as an experimental demonstration, Sb and Bi₂Te₃ thin films with closely matched in-plane lattice constants are chosen to form two complementary heterostructures: Sb overlayers on Bi₂Te₃ (Sb/Bi₂Te₃) and Bi₂Te₃ overlayers on Sb (Bi₂Te₃/Sb), with the overlayer thickness as a tuning parameter. In the bulk form, Sb (a semimetal) and Bi₂Te₃ (an insulator) both host TSSs with the same topological order but substantially different decay lengths and dispersions, whereas ultrathin Sb and Bi₂Te₃ films by themselves are fully gapped trivial insulators. Angle-resolved photoemission band mappings, aided by theoretical calculations, confirm the formation of emergent TSSs in both heterostructures. The energy position of the topological Dirac point varies as a function of overlayer thickness, but the variation is non-monotonic, indicating nontrivial effects in the formation of topological heterostructure systems. The results illustrate the rich physics of engineered composite topological systems that may be exploited for nanoscale spintronics applications.