Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

Brahlek, Matthew; Koirala, Nikesh; Bansal, Namrata; Oh, Seongshik

doi:10.1016/j.ssc.2014.10.021

Cited by 142 publications

(185 citation statements)

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“…When N b is smaller than 10 18 cm −3 , E F is pinned close to the conduction band minimum for an n-type material or similarly close to the valence band maximum for a p-type system [63]. For the surface region of either type of I(E,k) images arrived at by exposure of different compounds to residual gases in UHV (P < 2 × 10 −10 mbar) for time periods in the range of 10-48 h, during which external illumination of these specific sample locations was kept to a minimum and the downward band bending was seen to saturate (see also row 7 of Table I).…”

Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 88%

“…If the bulk carrier density increases, as is the case on going from the type-2 to the type-1 BSTS2 crystals, one would expect the the width of the space-charge region (SCR) to decrease for a given total band-bending potential. By means of parametric solutions of all equations related to the band bending and charge transfer, recently Brahlek et al provided contour plots showing the relation between the SCR and N bulk for 3D topological insulators [63].…”

Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 99%

“…The energy position of the Fermi level deep inside the bulk of a 3D topological insulator is determined by its bulk carrier density N b [63]. When N b is smaller than 10 18 cm −3 , E F is pinned close to the conduction band minimum for an n-type material or similarly close to the valence band maximum for a p-type system [63].…”

Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 99%

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Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

et al. 2015

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Topological insulators are a novel materials platform with high applications potential in fields ranging from spintronics to quantum computation. In the ongoing scientific effort to demonstrate controlled manipulation of their electronic structure by external means, i.e., the provision of knobs with which to tune properties, stoichiometric variation and surface decoration are two effective approaches that have been followed. In angleresolved photoelectron spectroscopy (ARPES) experiments, both approaches are seen to lead to electronic band-structure changes. Most importantly, such approaches result in variations of the energy position of bulk and surface-related features and the creation of two-dimensional electron gases. The data presented here demonstrate that a third manipulation handle is accessible by utilizing the amount of super-band-gap light a topological insulator surface has been exposed to under typical ARPES experimental conditions. Our results show that this third knob acts on an equal footing with stoichiometry and surface decoration as a modifier of the electronic band structure, and that it is in continuous and direct competition with the latter. The data clearly point towards surface photovoltage and photoinduced desorption as the physical phenomena behind modifications of the electronic band structure under exposure to high-flux photons. We show that the interplay of these phenomena can minimize and even eliminate the adsorbate-related surface band bending on typical binary, ternary, and quaternary Bi-based topological insulators. Including the influence of the sample temperature, these data set up a detailed framework for the external control of the electronic band structure in topological insulator compounds in an ARPES setting. Four external knobs are available: bulk stoichiometry, surface decoration, temperature, and photon exposure. These knobs can be used in conjunction to fine tune the band energies near the surface and consequently influence the topological properties of the relevant electronic states.

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Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 88%

Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 99%

Section: Comparison Of the Response Of The Various Ti Compounds Tomentioning

confidence: 99%

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Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

et al. 2015

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“…Thus, we conclude, the overwhelming majority of charge carriers originate from extrinsic dopants on the top and bottom interfaces while the bulk carrier density remains low. For small values of intrinsic doping and moderate surface doping, it was shown that (several) quantum-confined 2DEG bands form due to strong band-bending in the region where the surface charge is screened 19,[37][38][39] . However, it is unlikely that the depopulation of a single 2DEG band causes a steep drop in the critical current as the number of involved Andreev bound states (ABS) decreases ∼ k 2 with the magnitude of the wave vector k toward the bottom of the band.…”

Section: Discussionmentioning

confidence: 99%

Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

et al. 2016

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Topological insulators (TIs) hold great promise for topological quantum computation in solidstate systems. Recently, several groups reported experimental data suggesting that signatures of Majorana modes have been observed in topological insulator Josephson junctions (TIJJs). A prerequisite for the exploration of Majorana physics is to obtain a good understanding of the properties of low-energy Andreev bound states (ABS) in a material with topologically non-trivial band structure. Here, we present experimental data and a theoretical analysis demonstrating that the band structure inversion close to the surface of a TI has observable consequences for supercurrent transport in TIJJs prepared on surface-doped Bi 2 Se 3 thin films. Electrostatic carrier depletion of the film surface leads to an abrupt drop in the critical current of such devices. The effect can be understood as a relocation of low-energy ABS from a region deeper in the bulk of the material to the more strongly disordered surface which is driven by the topology of the effective band structure in the presence of surface dopants.

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“…Moreover, as we discussed earlier, in order to ensure the bulk insulating character of these low-carrier-density samples, it is critical to keep the sheet carrier densities substantially below 1 × 10 13 cm −2 and maintain upward (instead of downward) band bending near the surfaces. 16 Below, we show that in order to stabilize the low-carrier-density Bi 2 Se 3 films, it is essential to use proper capping layers. Among the three capping layers we studied, in situ-deposited In 2 Se 3 , in situ-deposited Se, and ex situ-deposited poly(methyl methacrylate) (PMMA), only Se and PMMA exhibited good stabilization effect.…”

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confidence: 88%

Stability of low-carrier-density topological-insulator Bi₂Se₃ thin films and effect of capping layers

et al. 2015

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Although over the past number of years there have been many advances in the materials aspects of topological insulators (TI), one of the ongoing challenges with these materials is the protection of them against aging. In particular, the recent development of low-carrier-density bulk-insulating Bi2Se3 thin films and their sensitivity to air demands reliable capping layers to stabilize their electronic properties. Here, we study the stability of the low-carrier-density Bi2Se3 thin films in air with and without various capping layers using DC and THz probes. Without any capping layers, the carrier density increases by ~150% over a week and by ~280% over 9 months. In situ-deposited Se and ex situ-deposited Poly(methyl methacrylate) (PMMA) suppresses the aging effect to ~27% and ~88% respectively over 9 months. The combination of effective capping layers and low-carrierdensity TI films will open up new opportunities in topological insulators.

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Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

Cited by 142 publications

References 50 publications

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

Stability of low-carrier-density topological-insulator Bi₂Se₃ thin films and effect of capping layers

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Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

Cited by 142 publications

References 50 publications

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

Dirac states with knobs on: Interplay of external parameters and the surface electronic properties of three-dimensional topological insulators

Signature of a topological phase transition in the Josephson supercurrent through a topological insulator

Stability of low-carrier-density topological-insulator Bi2Se3 thin films and effect of capping layers

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Stability of low-carrier-density topological-insulator Bi₂Se₃ thin films and effect of capping layers