Abstract
Quantum Hall (QH) and quantum spin Hall (QSH) phases have very different edge states and, when going from one phase to the other, the direction of one edge state must be reversed. We study this phenomenon in graphene in the presence of a strong perpendicular magnetic field on top of a spin-orbit (SO)-induced QSH phase. We show that, below the SO gap, the QSH phase is virtually unaffected by the presence of the magnetic field. Above the SO gap, the QH phase is restored. An electrostatic gate placed on top of the system allows the creation of a QSH-QH junction which is characterized by the existence of a spin-polarized chiral state, propagating along the topological interface. We find that such a setup naturally provides an extremely sensitive spin-polarized current switch which could pave the way to novel spin-based electronic devices.Received 24 January 2012DOI:https://doi.org/10.1103/PhysRevX.2.031004This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.Published by the American Physical Society
Highlights
Electronic properties of graphene and topological insulators have received considerable attention these last few years [1,2]
We turn to the investigation of the transport properties of a junction between a quantum spin Hall (QSH) and a Quantum Hall (QH) phase [Fig. 1(c)]. We show that this setup features a robust state, localized at the interface between the two topological insulators, analogous to the ambipolar ‘‘snake’’ states that arise in graphene quantum Hall n-p junctions [19], and take advantage of this state by demonstrating how it can serve to realize a topologically protected spinpolarized charge-current switch
It can be summarized in very simple terms: For Fermi energies inside the SO gap jEFj < Áso, the system is in the QSH phase, with opposite spin channels on a given edge propagating in opposite directions, while for energies jEFj > Áso, the system is in the QH phase, with opposite spin channels on a given edge propagating in the same direction
Summary
Electronic properties of graphene and topological insulators have received considerable attention these last few years [1,2]. These exotic quasiparticles carry a topological Berry phase which has been shown to give rise to many unusual transport phenomena such as the suppression of backscattering ( known as Klein tunnelling) [3,4], weak antilocalization [5,6], and a ‘‘relativistic’’ quantum Hall effect [7,8,9] Some of these properties, are not robust to the presence of disorder—as soon as the latter is sufficiently short ranged to induce valley mixing—due to the existence in graphene of an even number of Dirac cones. There, we discuss similarities with other setups such as quantum Hall n-p junctions, and comment on the possibility of realizing a spin-polarized current
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