Abstract
Topological insulators are a new class of matter characterized by the unique electronic properties of an insulating bulk and metallic boundaries arising from non-trivial bulk band topology. While the surfaces of topological insulators have been well studied, the interface between topological insulators and semiconductors may not only be more technologically relevant, but the interaction with non-topological states may fundamentally alter the physics. Here, we present a general model to show that this type of interaction can lead to vertical twinning of the Dirac cone, whereby the hybridized non-spin-degenerate interfacial states cross twice as they span the bulk bandgap. This hybridization leads to spin-momentum locking of non-topological states with either helical (clockwise or anticlockwise) or even anti-helical (negative winding number) spin orientation depending on the parametization of the interaction. Model results are corroborated by first-principles calculations of the technologically relevant Bi2Se3 film van der Waals bound to a Se-treated GaAs substrate.
Highlights
Topological insulators are a new class of matter characterized by the unique electronic properties of an insulating bulk and metallic boundaries arising from non-trivial bulk band topology
The relatively small bandgap and large spin–orbit interaction in Topological insulators (TIs) lead to the non-trivial topology and a Z2 invariant, which is distinct from normal insulators (NIs) such as GaAs, Si or even vacuum
The pristine TI states at the interface are described by a massless Dirac cone with helical spin textures represented by the effective surface
Summary
Topological insulators are a new class of matter characterized by the unique electronic properties of an insulating bulk and metallic boundaries arising from non-trivial bulk band topology. We present a general model to show that this type of interaction can lead to vertical twinning of the Dirac cone, whereby the hybridized non-spin-degenerate interfacial states cross twice as they span the bulk bandgap. It is believed that interfacial topological states are spin–momentum locked, where the spin polarization of the electron is locked in plane and perpendicular to the crystal momentum, k, leading to a number of potential applications[11,12] They may find great use in spintronics, as the spin current can be controlled without magnetism, but instead through the application of electric fields leading to new architectures for spin-based transistors[13,14,15]. We construct a simple model Hamiltonian to describe the interaction of the topological interface state with nontopological states and use first-principles density functional theory (DFT) to calculate the band structure and spin texture of the prototypical semiconducting/TI interface, GaAs/Bi2Se3. We find that the type of interaction depends strongly on both the band offset between the TI and semiconductor as well as the chemical nature of the interface, suggesting that novel optical and electronic phenomena can be achieved through chemical modification of the interface
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