Interaction and disorder effects in three-dimensional topological insulator thin films

König, Elio J.; Ostrovsky, P. M.; Protopopov, I. V.; Gornyi, I. V.; Burmistrov, I. S.; Mirlin, A. D.

doi:10.1103/physrevb.88.035106

Cited by 24 publications

(27 citation statements)

References 125 publications

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“…The most striking is the fact that these surface states are described by a Dirac Hamiltonian [1,2], which gives rise to weak antilocalization (WAL) in the presence of scalar disorder [3][4][5]. The WAL correction can be affected by the interaction of the surface states with the residual bulk states [6], the thickness of the film [7], or electron-electron interactions [8,9] changing its sign and turning it into weak localization (WL). At the same time, since 3DTIs have strong spin-orbit coupling, one expects spin-orbit coupled impurities to have a strong effect on transport, different however than in graphene where two valleys are present [10,11].…”

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confidence: 99%

Conductivity corrections for topological insulators with spin-orbit impurities: Hikami-Larkin-Nagaoka formula revisited

et al. 2015

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The Hikami-Larkin-Nagaoka (HLN) formula [Prog. Theor. Phys. 63, 707 (1980)] describes the quantum corrections to the magnetoconductivity of a quasi-2D electron gas (quasi-2DEG) with parabolic dispersion. It predicts a crossover from weak localization to antilocalization as a function of the strength of scattering off spin-orbit impurities. Here, we derive the conductivity correction for massless Dirac fermions in 3D topological insulators (3DTIs) in the presence of spin-orbit impurities. We show that this correction is always positive and therefore we predict weak antilocalization for every value of the spin-orbit disorder. Furthermore, the correction to the diffusion constant is surprisingly linear in the strength of the impurity spin-orbit. Our results call for a reinterpretation of experimental fits for the magnetoconductivity of 3D TIs which have so far used the standard HLN formula.PACS numbers: 73.20.Fz, 73.43.Qt, 73.25.+i Introduction. The problem of the diffusion of the surface states of 3DTIs is a complex one due to a variety of competing phenomena. The most striking is the fact that these surface states are described by a Dirac Hamiltonian [1,2], which gives rise to weak antilocalization (WAL) in the presence of scalar disorder [3][4][5]. The WAL correction can be affected by the interaction of the surface states with the residual bulk states [6], the thickness of the film [7], or electron-electron interactions [8,9] changing its sign and turning it into weak localization (WL). At the same time, since 3DTIs have strong spin-orbit coupling, one expects spin-orbit coupled impurities to have a strong effect on transport, different however than in graphene where two valleys are present [10,11]. Surprisingly this problem has received virtually no attention [12] and so far the Dirac nature of the states, that manifest itself in the angular dependence of the Green functions, has not been taken into account in studies of spin-orbit impurities [7]. The problem is even more complicated in a transverse magnetic field.The formula commonly used to fit the magnetoconductance experiments on 3DTIs [13][14][15][16][17][18][19][20] was derived by Hikami, Larkin and Nagaoka (HLN) [21]. The HLN formula, however, lacks important features relevant to 3DTIs: it is derived for quasi-2DEGs with a parabolic electron dispersion (impurities are treated as threedimensional objects), so it accounts neither for the Dirac nature of the surface states nor for their strictly twodimensional character. Fig. 1 is the main result of this paper, and shows the different effects of spin-orbit scatter- * The two first authors contributed equally.† Author to whom correspondence should be addressed : hankiewicz@physik.uni-wuerzburg.de ing for the HLN formula, namely WL to WAL crossover with the strength of spin-orbit impurity scattering, and for Dirac fermions, where WAL appears regardless of the strength of spin-orbit impurities. We only observe a convergence of the two formulas for large values of the strength of the impurity spin-orbit sc...

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confidence: 99%

Conductivity corrections for topological insulators with spin-orbit impurities: Hikami-Larkin-Nagaoka formula revisited

et al. 2015

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“…One may notice that there is a weak upturn in all three curves at the lowest temperatures; such an upturn has been reported for TI thin films in the past, [25][26][27] and is discussed to be due to electron interaction effects. 28,29 The R yx (B) curves showed significant and complicated changes when V g is varied. In Fig.…”

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confidence: 99%

Top gating of epitaxial (Bi1−xSbx)2Te3 topological insulator thin films

Yang

Taskin

Sasaki

et al. 2014

Applied Physics Letters

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The tunability of the chemical potential for a wide range encompassing the Dirac point is important for many future devices based on topological insulators. Here we report a method to fabricate highly efficient top gates on epitaxially grown (Bi1−xSbx)2Te3 topological insulator thin films without degrading the film quality. By combining an in situ deposited Al2O3 capping layer and a SiNx dielectric layer deposited at low temperature, we were able to protect the films from degradation during the fabrication processes. We demonstrate that by using this top gate, the carriers in the top surface can be efficiently tuned from n-to p-type. We also show that magnetotransport properties give evidence for decoupled transport through top and bottom surfaces for the entire range of gate voltage, which is only possible in truly bulk-insulating samples.Topological insulators (TIs) are a class of insulators possessing an energy gap in the bulk and helically spinpolarized gapless states on the surface. [1][2][3] In the last few years, great efforts and progress have been made to synthesize high-quality, bulk-insulating TI materials in various ways. [4][5][6][7][8][9][10][11][12][13] . As the materials issues being solved, the focus and interest of experimentalists start to shift to the realization of the theoretically proposed TI devices for applications ranging from spintronics to quantum computing. 1-3 For such devices, an efficient gate control to tune the Fermi level in a wide range is usually essential, and already many gating experiments have been done on TI materials by using different gating techniques. [12][13][14][15][16][17][18][19][20] Among the various gating techniques, top gating has an advantage to provide local control of the chemical potential, which is favorable in many applications. However, a damage-free method to fabricate efficient top gates on TIs has not yet been fully developed.To achieve efficient top-gate controls of TI materials, there are two main difficulties. One is to obtain bulkinsulating samples, because the unwanted bulk carriers bring the Fermi level far away from the Dirac point and screen the electric field. This difficulty is being solved by means of chemical doping, in both single crystals 4-10,12,13 and thin films. 11 The other difficulty is the degradations of the sample surface during the fabrication processes, especially during the deposition of the dielectric material. It has been shown that the usual methods to deposit dielectric materials such as atomic layer deposition (ALD) can cause heavy damage to the TI surface; 15 such a damage would lower the surface mobility and also introduce a large number of impurity states to pin the surface chemical potential, making its gate tuning to be difficult. 15 It is thus important to develop a method to fabricate top gates with minimal damage to the TI surface.In this Letter, we report our top-gating results on (Bi 1−x Sb x ) 2 Te 3 topological-insulator thin films grown by molecular beam epitaxy (MBE). Following Ref. 11, the composition of ...

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“…We showed that the half-metallic behavior can lead to a pseudospin-valve-like effect in the tunneling current between two TI surfaces, which can be used as a diagnostic for the half-metallic behavior. Our study indicates that weak disorder (which could get induced due to the roughness in surface potentials) can not only affect transport due to scattering of electron due to its coupling with the spin degree of freedom of the disorder potential (which is the one usually considered for study [21]) but also due to its coupling with the frozen pseudospin degree of freedom of the disorder potential. Presence of such disorder may not be seen in the traditional methods used to probe surface states which couple only to the spin texture of the surface states such as the spin polarized ARPES and STM.…”

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confidence: 81%

Pseudospin-valve effect on transport in junctions of three-dimensional topological insulator surfaces

2016

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We show that the surface states of pristine 3D topological insulators (TIs) are analogs of ferromagnetic half metals due to complete polarization of an emergent momentum independent pseudospin (SU(2)) degree of freedom on the surface. To put this claim on firm footing, we present results for TI surfaces perpendicular to the crystal growth axis, which clearly show that the tunneling conductance between two such TI surfaces of the same TI material is dominated by this half metallic behavior leading to physics reminiscent of a spin-valve. Further using the generalized tunnel magnetoresistance derived in this work we also study the tunneling current between arbitrary TI surfaces. We also perform a comprehensive study of the effect of all possible surface potentials allowed by time reversal symmetry on this spin-valve effect and show that it is robust against most of such potentials.

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Interaction and disorder effects in three-dimensional topological insulator thin films

Cited by 24 publications

References 125 publications

Conductivity corrections for topological insulators with spin-orbit impurities: Hikami-Larkin-Nagaoka formula revisited

Conductivity corrections for topological insulators with spin-orbit impurities: Hikami-Larkin-Nagaoka formula revisited

Top gating of epitaxial (Bi1−xSbx)2Te3 topological insulator thin films

Pseudospin-valve effect on transport in junctions of three-dimensional topological insulator surfaces

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