Gigantic negative magnetoresistance in the bulk of a disordered topological insulator

Breunig, Oliver; Wang, Zhiwei; Taskin, A. A.; Lux, Jonathan; Rosch, Achim; Ando, Yoichi

doi:10.1038/ncomms15545

Cited by 88 publications

(83 citation statements)

References 38 publications

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“…Fermi energies close to the Dirac point) as in this regime the resulting magnetoresistance becomes linear. Comparing our findings with experimental results, we note that linear magnetoresistance is very common in measurements on topological surface states [1][2][3][4][5][6][7]. However, distinguishing the described effect from classical magnetoresistance arising from strong inhomogeneity [12,13] may be difficult.…”

Section: Surface Dirac Conessupporting

confidence: 61%

Magnetoresistance from time-reversal symmetry breaking in topological materials

2019

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Magnetotransport measurements are a popular way of characterizing the electronic structure of topological materials and often the resulting datasets cannot be described by the well-known Drude model due to large, non-parabolic contributions. In this work, we focus on the effects of magnetic fields on topological materials through a Zeeman term included in the model Hamiltonian. To this end, we re-evaluate the simplifications made in the derivations of the Drude model and pinpoint the scattering time and Fermi velocity as Zeeman-term dependent factors in the conductivity tensor. The driving mechanisms here are the aligment of spins along the magnetic field direction, which allows for backscattering, and a significant change to the Fermi velocity by the opening of a hybridization gap. After considering 2D and 3D Dirac states, as well as 2D Rashba surface states and the quasi-2D bulk states of 3D topological insulators, we find that the 2D Dirac states on the surfaces of 3D topological insulators produce magnetoresistance, that is significant enough to be noticable in experiments. As this magnetoresistance effect is strongly dependent on the spin-orbit energy, it can be used as a telltale sign of a Fermi energy located close to the Dirac point.

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Section: Surface Dirac Conessupporting

confidence: 61%

Magnetoresistance from time-reversal symmetry breaking in topological materials

2019

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“…[29,31,32] The lowered spin relaxation length in CVD graphene is primarily due to the presence of metallic adatoms such as copper, increasing the SOC. [43,44] Small variations of the surface composition can be a cause of such puddles. [42] Furthermore, the electronic band structure of BSTS may in practice be more complex than it is often drawn theoretically.…”

Section: Resultsmentioning

confidence: 99%

Spin‐Momentum Locking in the Gate Tunable Topological Insulator BiSbTeSe₂ in Non‐Local Transport Measurements

Voerman

Huang

et al. 2019

Adv Elect Materials

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The helical spin‐momentum locking of an electron in a topological surface state is a feature excellently suited for the use in spintronic applications. Devices are fabricated that allow to generate, transport, and detect the spin‐polarization coming from an electronic current in the topological surface state of BiSbTeSe2; a topological insulator reported to have a negligible bulk contribution to its conduction. The successful creation of such a device is described, as is a study of the generated spin‐polarized current as the BiSbTeSe2 surface state is gated through its Dirac point. A non‐local voltage difference across separated ferromagnetic leads is observed, larger than previously reported in literature. The spin‐polarization has a maximum when the Fermi level crosses the Dirac point.

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“…Also, puddles can explain the coexistence of electron-type and hole-type carriers in compensated samples [9] and the small activation energy observed in dc resistivity data [5]. Intriguingly, puddles are further found to be responsible for the surprising effect of gigantic negative magnetoresistance reported for TlBi 0.15 Sb 0.85 Te 2 [10]. In this context, novel magneticfield effects would be expected in the vicinity of the cutoff frequency ν c .…”

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confidence: 86%

Large positive magnetoconductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

et al. 2019

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The bulk electronic properties of compensated topological insulators are strongly affected by the self-organized formation of charge puddles at low temperature, but their response in the microwave frequency range is little studied. We employed broadband impedance spectroscopy up to 5 GHz to address the ac transport properties of well-compensated BiSbTeSe2, where charge puddles are known to form as metallic entities embedded in an insulating host. It turns out that the average puddle size sets the characteristic frequency νc in the GHz range, across which the insulating dc behavior is separated from a metal-like high-frequency response of delocalized carriers within the puddles. This νc is found to be controlled by a magnetic field, giving rise to a large positive magneto-conductivity observable only in the GHz range. This curious phenomenon is driven by the Zeeman energy which affects the local band filling in the disordered potential landscape to enhance the puddle size.One of the most prominent features of topological insulators is the spin-momentum locking in the surface states [1], which is particularly useful for spintronic applications [2]. To efficiently utilize the spin-momentum-locked surface states in applications, one should get rid of the residual bulk conduction, and this has been achieved by carefully compensating residual donors by residual acceptors through composition tuning in the Bi x Sb 2−x Te y Se 3−y compound [1,3,4]. Although such compensated topological insulators show reasonably high bulk insulation in dc, it has been elucidated that their transport properties are not only determined by the topologically protected surface states but also by the presence of charge puddles in the bulk [5], particularly at finite frequencies up to the infrared range [6]. This is because the Coulomb disorder of the randomly distributed charged donors and acceptors gives rise to potential fluctuations which grow as √ R in a volume of size R 3 [5, 7]; this inevitably leads to the self-organized formation of charge puddles on a mesoscopic length scale L at low temperatures. On this length scale, portions of a sample contain delocalized charge carriers which give rise to a Drude-like contribution to the optical conductivity σ (ν) above the Thouless cut-off frequency 2πν c = D/L 2 [6]. This cut-off is given by the time scale needed to diffuse through a puddle with the diffusion constant D. Using a simple scaling argument [5,7], L ≈ 100 − 500 nm is expected on the basis of infrared data [6]. This corresponds to ν c in the GHz range.Since the current-day information technology operates in the GHz range, understanding the microwave response of topological-insulator materials would be of crucial importance for their future applications in spintronics; nevertheless, the role of puddles in the transport properties in the GHz range has not yet been studied. This work is conceived to address this lack of understanding. At low temperature, the Drude-like puddle contribution to σ (ν) and its discrepancy with the dc conducti...

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Gigantic negative magnetoresistance in the bulk of a disordered topological insulator

Cited by 88 publications

References 38 publications

Magnetoresistance from time-reversal symmetry breaking in topological materials

Magnetoresistance from time-reversal symmetry breaking in topological materials

Spin‐Momentum Locking in the Gate Tunable Topological Insulator BiSbTeSe₂ in Non‐Local Transport Measurements

Large positive magnetoconductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

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Gigantic negative magnetoresistance in the bulk of a disordered topological insulator

Cited by 88 publications

References 38 publications

Magnetoresistance from time-reversal symmetry breaking in topological materials

Magnetoresistance from time-reversal symmetry breaking in topological materials

Spin‐Momentum Locking in the Gate Tunable Topological Insulator BiSbTeSe2 in Non‐Local Transport Measurements

Large positive magnetoconductivity at microwave frequencies in the compensated topological insulator BiSbTeSe2

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Product

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Spin‐Momentum Locking in the Gate Tunable Topological Insulator BiSbTeSe₂ in Non‐Local Transport Measurements