Strain effects in topological insulators: Topological order and the emergence of switchable topological interface states in Sb2Te3/Bi2Te3

Abstract

We investigate the effects of strain on the topological order of the Bi2Se3 family of topological insulators by ab-initio first-principles methods. Strain can induce a topological phase transition and we present the phase diagram for the 3D topological insulators, Bi2Te3, Sb2Te3, Bi2Se3 and Sb2Se3, under combined uniaxial and biaxial strain. Their phase diagram is universal and shows metallic and insulating phases, both topologically trivial and non-trivial. In particular, uniaxial tension can drive the four compounds into a topologically trivial insulating phase. We propose a Sb2Te3/Bi2Te3 heterojunction in which a strain-induced topological interface state arises in the common gap of this normal insulator-topological insulator heterojunction. Unexpectedly, the interface state is confined in the topologically trivial subsystem and is physically protected from ambient impurities. It can be switched on or off by means of uniaxial strain and therefore Sb2Te3/Bi2Te3 heterojunctions provide a topological system which hosts tunable robust helical interface states with promising spintronic applications.

Strain-driven tunable topological states in Bi2Se3

“…The gap is as large as 135meV for the system with a single TI QL. The TIS-TIS hybridization is similar to the TSS-TSS coupling found in TI thin films [26,43]. If we instead keep the thickness of the TI subsystem fixed to m=6QLs and we decrease the thickness of the NI to n=2 and 1 QLs-figures 3(h) and (i), respectively-, we find that a gap is also opened.…”

“…The system shows strong chemical bonding between adjacent layers within the QL, while the inter-QL coupling is of the weak vdW kind. The effect of uniaxial strain on bulk Bi 2 Se 3 has been addressed in a previous work [26] and is summarized in figure 1. Tensile strain along the (0001) direction shifts the Se (Bi) p z bands around the Γ point towards lower (higher) energies, eventually leading to a band uninversion.…”

“…In this article we exploit this idea to build topological homojunctions (THs), i.e., junctions composed of the same material in different topological phases. In all the systems discussed in this work we have fixed the in-plane lattice parameter to its equilibrium value a=4.17 Å [26], and the stacking sequence of the ideal bulk is maintained in all cases throughout the homojunctions. The vdW gap between two QLs with different strain values is taken as the average vdW gap of the two subsystems.…”

“…In fact, the transition from the topological to the trivial phase was predicted to occur for these bulk materials under purely uniaxial strain [19][20][21][22][23][24][25]. In a recent work, we investigated the combined effect of both uniaxial and biaxial strain on the topology of the Bi 2 Se 3 family and found a universal phase diagram [26]. All the compounds can exhibit metallic and insulating phases, both topologically trivial and non-trivial, and uniaxial tensile strain applied in the (0001) direction triggers a TPT, the critical strain being compound dependent.…”

Recent Advances in van der Waals Heterojunctions Based on Semiconducting Transition Metal Dichalcogenides

“…[78][79][80][81][82] Different than ordinary insulators, TIs have a bandgap in the bulk with a conductive surface state. [78][79][80][81][82] Different than ordinary insulators, TIs have a bandgap in the bulk with a conductive surface state.…”