Heavy Dirac fermions in a graphene/topological insulator hetero-junction

Abstract

The low energy physics of both graphene and surface states of three-dimensional topological insulators is described by gapless Dirac fermions with linear dispersion. In this work, we predict the emergence of a "heavy" Dirac fermion in a graphene/topological insulator hetero-junction, where the linear term almost vanishes and the corresponding energy dispersion becomes highly non-linear. By combining ab initio calculations and an effective low-energy model, we show explicitly how strong hybridization between Dirac fermions in graphene and the surface states of topological insulators can reduce the Fermi velocity of Dirac fermions. Due to the negligible linear term, interaction effects will be greatly enhanced and can drive "heavy" Dirac fermion states into the half quantum Hall state with non-zero Hall conductance.

Electronic Coupling between Graphene and Topological Insulator Induced Anomalous Magnetotransport Properties

“…1b These observations can be understood in the framework of the graphene-TI proximity effect that was theoretically predicted via band calculations in Refs. [8][9][10][11]. Under the magnetic field perpendicular to the graphene plane, the unevenly spaced energy spectrum is expressed as = ( )√2 ℏ 2 | | , where ℏ is reduced Planck's constant, the Fermi velocity is ~10 6 ⁄ , and the LL index N is positive for electrons and negative for holes [12,13].…”

“…3b,c. In the classical regime, the two-carrier model can be used to describe a zero-gap conductor with the same mobility for electrons and holes, giving Predicted by theoretical models [8][9][10][11], graphene can inherit spin-orbital textures from TI surface states near the Dirac point due to the proximity effect. Accordingly, we summarize the reforming band structures of graphene hybridized with TI surface in Fig.…”

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/ 31Graphene and surface states of topological insulators (TIs) can be described by two-dimensional (2D) massless Dirac Hamiltonian at the low energy excitations, which can be further modulated by adatom adsorption or interfacing with other functional materials [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Owing to the high carrier mobility and unique spin textures, TIs and graphene are promising for high speed electronics and spintronics [16].

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“…Owing to the high carrier mobility and unique spin textures, TIs and graphene are promising for high speed electronics and spintronics [16]. Recent theories [8][9][10][11] have predicted the hybridization of graphene and TIs can create nontrivial spin textures in graphene, even leading to quantum spin Hall states [1]. Generally, the rigorous √3 × √3 supercell of graphene stacked with TI is adopted in the calculations [8][9][10][11].…”

“…Such as, one of the topological states long sought in graphene is quantum spin Hall phase may be realized in topological insulator/graphene/topological insulator sandwiched system, which has been theoretically investigated [8]. Different from the asymmetric graphene/topological insulator configuration [9][10][11], the wavefunctions in graphene sandwiched by TIs can be hybridized with two TI surfaces. With an intrinsic bulk bandgap, the two-dimensional topological states may emerge in graphene-TI hybrid device.…”