Magnetotransport and weak anti-localization signatures in band-engineered 3D topological insulator pn-heterostructures

To experimentally harness the novel physics arising from topological surface states (TSS) in 3D topological insulators (3D TIs) it is crucial to develop control over key band structure parameters. At the same time, controlling the contribution of bulk bands to transport has represented a major experimental challenge.
In this contribution, we combine band structure engineering in Bi-based heterostructures with alloy composition-tuning to provide experimental access to single TSS. In a vertical pn-heterostructure of 3D TIs, intrinsic band bending is introduced to create an internal depletion zone. It will not only induce compensation of unintentional charges, but also lead to an isolation of the top TSS from parasitic bulk background. We present pn-heterostructures with (Bi_1-xSb_x)₂(Te_1-ySe_y)₃ as the p-type layer. Varying (x,y) provides extensive control over the position of the Dirac point and the Fermi level. Moreover we observe a significant reduction of bulk carriers, compared to e.g. Bi₂Se₃. We analyze our heterostructures in magnetotransport and angle-resolved photoemission spectroscopy (ARPES). Furthermore we discuss our conclusions in the light of the Hikami-Larkin-Nagaoka theory for weak anti-localization signatures observed in the longitudinal magneto-resistance.