Enhancement in surface mobility and quantum transport of Bi2−xSbxTe3−ySey topological insulator by controlling the crystal growth conditions

Han, Kyu Bum; Chong, Su Kong; Oliynyk, Anton O.; Nagaoka, Akinobu; Petryk, Suzanne; Scarpulla, Michael A.; Deshpande, Vikram V.; Sparks, Taylor D.

doi:10.1038/s41598-018-35674-z

Cited by 23 publications

(18 citation statements)

References 34 publications

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“…The boundaries around the overall CNP are traced by dashed lines and labeled with the LL indices of top ( N t ) and bottom ( N b ) surfaces in longitudinal conductivity (σ xx ) maps in Figure a. Hall conductivity (σ xy ) (Figure b) develops into rhombus-shaped QH plateaus at integer LL filling factors (ν), corresponding to the sum of half-integers for each surface (ν = ν t + ν b = ( N t + 1/2) + ( N b + 1/2)), ,, in the σ xx minima regions. The four quadrants are assigned to two symmetric ν = 0 (white); and antisymmetric ν = −1 (blue) and +1 (red) QH plateaus.…”

Section: Resultsmentioning

confidence: 99%

“…Bottom hBN/Gr layers were transferred onto the substrate, followed by annealing in Ar/H2 environment at 360-380 o C for 2 hours to provide a clean base for BSTS. BSTS thin flakes were exfoliated from a bulk crystal grown by a vertical Bridgman furnace, 26 and transferred onto the hBN/Gr using the transfer stage. The contact electrodes were made using a standard electron beam lithography process, followed by Cr/Au (2 nm/25 nm) deposition in an electron beam evaporator.…”

Section: Methodsmentioning

confidence: 99%

“…(a). Hall conductivity (σxy) (Fig.3(b)) develops into rhombus-shaped QH plateaus at integer LL filling factors (ν), corresponding to the sum of half-integers for each surface (ν= νt+νb = (Nt+½)+(Nb+½)),4,6,26 in the σxx minima regions. The four quadrants are assigned to two symmetric ν= 0 (white); and antisymmetric ν= -1 (blue) & +1 (red) QH plateaus.…”

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Landau Levels of Topologically-Protected Surface States Probed by Dual-Gated Quantum Capacitance

et al. 2019

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Spectroscopy of discrete Landau levels (LLs) in bulk-insulating three-dimensional topological insulators (3D TIs) in perpendicular magnetic field characterizes the Dirac nature of their surface states. Despite a number of studies demonstrating the quantum Hall effect (QHE) of topological surface states, quantitative evaluation of the LL energies, which serve as fundamental electronic quantities for study of the quantum states, is still limited. In this work, we explore the density of states of LLs by measuring quantum capacitance (CQ) in a truly bulk insulating 3D TI via a van der Waals heterostructure configuration. By applying dual gate voltages, we access the individual surface states' LLs and extract their chemical potentials to quantify the LL spacings of each 2 surface. We evaluate the LLs' energies at two distinguished QH states, namely dissipationless (ν= ±1) and dissipative (ν= 0) states in the 3D TI. KEYWORDStopological insulators, quantum capacitance, Landau levels, van der Waals heterostructures, quantum Hall effect The topologically-protected linearly dispersing surface states of three-dimensional topological insulators (3D TIs) offer a route for exploration of quantum phenomena such as the topological exciton superfluid, fractional charges and Majorana fermions in quantum regimes. 1-3 In a strong perpendicular magnetic field, the surface Dirac fermions localize in cyclotron orbits, forming discrete energy states known as Landau levels (LLs). This gives rise to the quantum Hall effect (QHE) in magnetotransport, where the Hall conductivity is quantized at integers as a result of halfintegers from each (top and bottom) surface. 4-6 Alternatively, quantum capacitance (CQ) can also be exploited to study the LLs electronically. 7-10 Different from quantum transport which is only sensitive to edge modes, CQ provides a probe of the charge states in the bulk of the surfaces. CQ is an ideal measure of the thermodynamic density of states (DoS) for low carrier density and gate-tunable materials. 8-10 Nevertheless, it is relatively less explored in 3D TIs in the past as compared to quantum transport primarily due to the shortcoming of a proper 3D TI candidate.Previous studies of CQ in Bi2Se3 revealed the Dirac-like surface states 11 and Shubnikov-de Haaslike quantum oscillations in magnetic field. 12 However, Bi2Se3 is known to exhibit substantial carrier doping in bulk, and extra trapped states induced by intrinsic defects. 11,13 More recently, CQ in high mobility 3D TI based on strained HgTe was reported, 14 showing more intrinsic bulk band and clear LL quantization. Yet, the narrow bulk bandgap in strained HgTe (~20 meV), which is

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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confidence: 99%

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Landau Levels of Topologically-Protected Surface States Probed by Dual-Gated Quantum Capacitance

et al. 2019

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“…The growth was carried out by placing the ampoule vertically 10 cm above the center of zone A, and passed down the three hot-zones at an extremely slow rate (6 mm/day). More details on the setup and synthesis methods can be found in the references 26 TEM cross-section specimens were prepared using a FEI Helios NanoLabTM 650 focused ion beam dual beam microscope. The three layers samples were coated with about 100 nm of amorphous carbon, followed by a thick Pt coating to protect exposed area before cross-sectioning.…”

Section: Methodsmentioning

confidence: 99%

Topological Insulator-Based van der Waals Heterostructures for Effective Control of Massless and Massive Dirac Fermions

et al. 2018

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Three dimensional (3D) topological insulators (TIs) are an important class of materials with applications in electronics, spintronics and quantum computing. With the recent development of truly bulk insulating 3D TIs, it has become possible to realize surface dominated phenomena in electrical transport measurements e.g. the quantum Hall (QH) effect of massless Dirac fermions in topological surface states (TSS). However, to realize more advanced devices and phenomena, there is a need for a platform to tune the TSS or modify them e.g. gap them by proximity with magnetic insulators, in a clean manner. Here we introduce van der Waals (vdW) heterostructures in the form of topological

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“…Device fabrications. Variable thicknesses of hBSTS crystal flakes were exfoliated from the bulk crystal [36] and then transferred using a micromanipulator transfer stage into the heterostructures of Gr/hBN sandwiched layers. We fabricated the hBSTS devices into the Hall bar configuration with Cr/Au (2 nm/60 nm) as the contact electrodes.…”

Section: Methodsmentioning

confidence: 99%

Emergent Helical Edge States in a Hybridized Three-Dimensional Topological Insulator

Chong¹,

Liu²,

Watanabe³

et al. 2021

Preprint

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As the thickness of a three-dimensional (3D) topological insulator (TI) becomes comparable to the penetration depth of surface states, quantum tunneling between surfaces turns their gapless Dirac electronic structure into a gapped spectrum. Whether the surface hybridization gap can host topological edge states is still an open question. Herein, we provide transport evidence of 2D topological states in the quantum tunneling regime of a bulk insulating 3D TI BiSbTeSe2. Different from its trivial insulating phase, this 2D topological state exhibits a finite longitudinal conductance at ~2e2/h when the Fermi level is aligned within the surface gap, indicating an emergent quantum spin Hall (QSH) state. The transition from the QSH to quantum Hall (QH) state in a transverse magnetic field further supports the existence of this distinguished 2D topological phase. In addition, we demonstrate a second route to realize the 2D topological state via surface gap-closing and topological phase transition mechanism mediated by a transverse electric field. The experimental realization of the 2D topological phase in a 3D TI enriches its phase diagram and marks an important step toward functional topological quantum devices.

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Enhancement in surface mobility and quantum transport of Bi2−xSbxTe3−ySey topological insulator by controlling the crystal growth conditions

Cited by 23 publications

References 34 publications

Landau Levels of Topologically-Protected Surface States Probed by Dual-Gated Quantum Capacitance

Landau Levels of Topologically-Protected Surface States Probed by Dual-Gated Quantum Capacitance

Topological Insulator-Based van der Waals Heterostructures for Effective Control of Massless and Massive Dirac Fermions

Emergent Helical Edge States in a Hybridized Three-Dimensional Topological Insulator

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