Switching spin and charge between edge states in topological insulator constrictions

Abstract

Since the prediction of a new topological state of matter in graphene, materials acting as topological insulators have attracted wide attention. Shortly after the theoretical proposal for a mercury telluride (HgTe)-based two-dimensional topological insulator, the observation of the quantum spin Hall effect and non-local edge transport brought compelling experimental evidence for quantized conductance due to edges states. The spin orientation and propagation direction of such helical edge states are inherently connected, providing protection against backscattering. However, these features conversely render controlled spin operations such as spin switching difficult. Here we therefore propose constrictions as connectors between opposite edge (and spin) states in HgTe. We demonstrate how the coupling between edge states, which overlap in the constriction, can be employed both for steering the charge flow into different edge modes and for controlled spin switching. This gives rise to a three-state charge and spin transistor function. Unlike in a conventional spin transistor, the switching does not rely on a tunable Rashba spin-orbit interaction, but on the energy dependence of the edge state wavefunctions. Based on this mechanism, and supported by numerical transport calculations, we present two different ways to control spin- and charge-currents depending on the gating of the constriction.

References in corpus (8)

• Quantum Spin Hall Effect and Topological Phase Transition in HgTe Quantum Wells
• Quantum Spin Hall Insulator State in HgTe Quantum Wells
• Nonlocal edge state transport in the quantum spin Hall state
• Finite size effects of helical edge states in HgTe/CdTe quantum wells
• Full electrical control of Charge and Spin conductance through Interferometry of Edge States in Topological Insulators
• Revivals of quantum wave-packets in graphene
• Tunneling of Dirac electrons through spatial regions of finite mass
• Wave packet approach to transport in mesoscopic systems

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• Tunneling magnetoresistance devices based on topological insulators: Ferromagnet/insulator/topological-insulator junctions employing Bi${}_2$Se${}_3$
• Helical edge states in multiple topological mass domains
• Electronic quantum optics beyond the integer quantum Hall effect
• Noise and current correlations in tunnel junctions of Quantum Spin Hall edge states
• Controllable spin entanglement production in a quantum spin Hall ring
• $\pi$ Spin Berry Phase in a Quantum-Spin-Hall-Insulator-Based Interferometer: Evidence for the Helical Spin Texture of the Edge States
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• Transversal Propagation Behaviors of Helical Edge States In a QSH System
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• Interplay between Rashba interaction and electromagnetic field in the edge states of a 2D topological insulator
• Proposal for an ac spin current source
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• Interaction effects in non-equilibrium transport properties of a four-terminal topological corner junction
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• Probing spin entanglement by gate-voltage-controlled interference of current correlation in quantum spin Hall insulators
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• Volkov-Pankratov states on the edge of a quantum spin Hall system
• Determination of Out-of-plane Spin Polarization of Topological Surface States by Spin Hall Effect Tunneling Spectroscopy
• Lifting topological protection in a quantum spin Hall insulator by edge coupling
• Manipulation of helical states revealed by crossed Andreev reflection