Electronic Coupling between Graphene and Topological Insulator Induced Anomalous Magnetotransport Properties

Abstract

/ 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]. 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]. For the incommensurate graphene-TI stacking,Zhang et al. [10] suggested that the renormalized bands of hybrid graphene still acquire the in-plane spin textures from the surface states of TI even in the presence of surface roughness at the heterointerface. The coupling between graphene and TI has been pursued via the angle resolved photoemission spectroscopy (ARPES) Gate-tunable conductivity of the hybrid device is shown in Fig. 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]. The half-filled LLs, such as N = −3, −2, Fig. 3). We should realize that the possible coupling between graphene and TI surface states is the second (or higher) order effect [8][9][10][11]. The hopping process between the orbitals of carbon atoms in graphene and orbitals of the bottom surface states in Bi 2 Se 3 nanoribbons introduces significant influences on the transport properties in graphene near the Dirac point.Anomalous magnetotransport features at Dirac point. Now we discuss the magnetotransport at the Dirac point (or the zeroth LL) in the graphene hybrid device.The evolution of ( * ) curves near the Dirac point at various temperatures andunder negative magnetic fields is shown in Fig. 3a (see Supplementary Fig. 4 for the evolution of ( * )). The curves are shifted for clarity. The resistivity at the Dirac point ( ) versus B is extracted and shown in Fig. 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. 4. As the interaction between graphene and TI is significant, the fourfold degeneracy of the original graphene bands (Fig. 4a) is par...

Spin Proximity Effects in Graphene/Topological Insulator Heterostructures

“…26 Additionally, the fact that electronic states in Gr/TMDC sys-tems are spin-polarized primarily along the outof-plane direction 27 results in large spin lifetime anisotropy between in-plane and out-ofplane spin-polarized electrons, which is however weakly energy dependent and therefore not tunable. [28][29][30] Recently, a lot of attention has been paid to heterostructures of graphene and topological insulators (TIs), with reports of anomalous magnetotransport, giant Edelstein effect, and gate-tunable tunneling resistance, [31][32][33][34][35] as well as the possible existence of a quantum spin Hall phase. 36,37 On the more applied side, the fabrication of broadband photodetectors based on Gr/TI heterostructures has been realized, 38 as well as the injection of spin-polarized current from an ultrathin Bi 2 Te 2 Se nanoplatelet into graphene.…”

Non-local electrical detection of spin-momentum-locked surface currents in the 3D topological insulator BiSbTeSe$_{2}$

“…In this technique, the local voltage-probes typically measure both surface and bulk transport. Previous studies of the spin-momentum locking and the peculiar spin textures of 3D-TIs were limited either to the direct probing of the top surface of the material or to indirect measurements of the spin texture of a buried 3D-TI surface by, for example, proximity coupling to other 2D materials such as graphene [46][47][48][49]. Our study demonstrates that the surface currents of a buried TI surface in contact to an insulator (SiO 2 in our case) can be directly measured by non-local transport configurations, which allows to probe spin-momentum locking of buried surfaces in more advanced van der Waals heterostructures.…”

Temperature-Dependent Raman Scattering of Large Size Hexagonal Bi2Se3 Single-Crystal Nanoplates

“…Bi 2 Se 3 , a typical thermoelectric material, has temperature evolution of Raman mode further relative to other two-dimensional materials, such as, the transition metal dichalcogenides (TMDCs) (MoS 2 , MoSe 2 , WS 2 , and WSe 2 ), black phosphorus, trichalcogenides ( TiS 3 ), which are summarized in Table 2. The calculated χ coefficient was listed in Table 2 and the χ of other materials were summarized for comparison, indicating the comparable χ coefficient and application of Bi 2 Se 3 nanoplates, and thus, our temperature-dependent Raman study can be exploited as large nonlocal signals to measure the temperature in graphene-Bi 2 Se 3 heterostructures device [53]. Table 2.…”