Interplay between Rashba Edge States and Topological Surface States in 3D Topological Insulators

Bismuth selenide (Bi₂Se₃) is a well-known material as a quantum spin Hall insulator with Dirac surface states protected by time-reversal symmetry. Recently, some screw dislocations in Bi₂Se₃ films and their electronic properties were observed by scanning tunneling microscopy. The thick, bulk-like films display increased local density of states confined at step edges, while the edge states disappear when the film thickness is reduced to three quintuples. We investigated the origin of experimentally measured thickness-dependent (topological) quantum states on Bi₂Se₃ using first-principles based modeling: They arise from the interaction between topological surface states and trivial states of Bi₂Se₃ with embedded 2D islands on the films. Our results illustrate that the charge and spin transport in the topological materials can be strongly influenced by the interaction between the topological and trivial states.