Emergent and Tunable Topological Surface States in Complementary Sb/Bi 2 Te 3 and Bi 2 Te 3 /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 Bi 2 Te 3 thin films with closely matched in-plane lattice constants are chosen to form two complementary heterostructures: Sb overlayers on Bi 2 Te 3 (Sb/Bi 2 Te 3 ) and Bi 2 Te 3 overlayers on Sb (Bi 2 Te 3 /Sb), with the overlayer thickness as a tuning parameter. In the bulk form, Sb (a semimetal) and Bi 2 Te 3 (an insulator) both host TSSs with the same topological order but substantially different decay lengths and dispersions, whereas ultrathin Sb and Bi 2 Te 3 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.