Imaging quantum spin Hall edges in monolayer WTe
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Shi, Yanmeng; Kahn, Joshua; Niu, Ben; Fei, Zaiyao; Sun, Bosong; Cai, Xinghan; Francisco, Brian; Wu, Di; Shen, Zhi‐Xun; Xu, Xiaodong; Cobden, David; Cui, Yong‐Tao

doi:10.1126/sciadv.aat8799

Cited by 147 publications

(122 citation statements)

References 32 publications

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“…16,[23][24][25][26][27][28][29][30][31][32] Specifically, monolayer WTe 2 has been identified theoretically to realize a QSH phase, 16,[33][34][35] and various experiments have verified its key features: an insulating bulk, the presence of conducting edge channels, and a quantized electronic conductance of 2e 2 /h over a large range of temperatures. [36][37][38][39][40][41][42] Furthermore, a magnetic field has been shown to lead to a breakdown of conductance in the investigated samples. 42 This suggests the opening of a Zeeman-type gap in the edge-state spectrum, contrary to other QSH insulator candidate materials.…”

Section: Introductionmentioning

confidence: 93%

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Lau

Ray

Varjas

et al. 2019

Phys. Rev. Materials

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We study the influence of sample termination on the electronic properties of the novel quantum spin Hall insulator monolayer 1T -WTe2. For this purpose, we construct an accurate, minimal 4-orbital tight-binding model with spin-orbit coupling by employing a combination of densityfunctional theory calculations, symmetry considerations, and fitting to experimental data. Based on this model, we compute energy bands and 2-terminal conductance spectra for various ribbon geometries with different terminations, with and without magnetic field. Because of the strong electron-hole asymmetry we find that the edge Dirac point is buried in the bulk bands for most edge terminations. In the presence of a magnetic field, an in-gap edge Dirac point leads to exponential suppression of conductance as an edge Zeeman gap opens, whereas the conductance stays at the quantized value when the Dirac point is buried in the bulk bands. Finally, we find that disorder in the edge termination drastically changes this picture: the conductance of a sufficiently rough edge is uniformly suppressed for all energies in the bulk gap regardless of the orientation of the edge. II. TIGHT-BINDING MODEL FOR MONOLAYER WTE2WTe 2 is a member of the transition metal dichalcogenide family of materials. Single layers in this materials class crystallize in a variety of polytypic structures such as the hexagonal 2H, the tetragonal 1T , and the distorted 1T structure. 16,44,45 While the former represent trivial semiconductors, the 1T configuration gives rise arXiv:1812.05693v3 [cond-mat.mes-hall]

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Section: Introductionmentioning

confidence: 93%

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Lau

Ray

Varjas

et al. 2019

Phys. Rev. Materials

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“…2,3 The experimental breakthrough leading to the 2D system was achieved in a strong spin-orbital coupled CdTe/HgTe quantum well, which gave rise to a quantum spin Hall state. 4 Recently, 1T′-WTe2 monolayer [5][6][7] has been proved to be a new quantum spin Hall insulator, with a conducting edge state that can survive to 100 K 8,9 , thereby offering a potential application for a 2D TI in ultra-low-energy electronics.…”

Section: Introductionmentioning

confidence: 99%

Quantum oscillations of robust topological surface states up to 50 K in thick bulk-insulating topological insulator

et al. 2019

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As personal electronic devices increasingly rely on cloud computing for energy-intensive calculations, the power consumption associated with the information revolution is rapidly becoming an important environmental issue. Several approaches have been proposed to construct electronic devices with low energy consumption. Among these, the low-dissipation surface states of topological insulators (TIs) are widely employed. To develop TI-based devices, a key factor is the maximum temperature at which the Dirac surface states dominate the transport behavior. Here, we employ Shubnikov-de Haas oscillations (SdH) as a means to study the surface state survival temperature in a high quality vanadium doped Bi1.08Sn0.02Sb0.9Te2S single crystal system. The temperature and angle dependence of the SdH show that: 1) crystals with different vanadium (V) doping levels are insulating in the 3 -300 K region; 2) the SdH oscillations show two-dimensional behavior, indicating that the oscillations arise from the pure surface states; and 3) at 50 K, the V0.04 single crystals (Vx:Bi1.08-xSn0.02Sb0.9Te2S, where x = 0.04) still show clear sign of SdH oscillations, which demonstrate that the surface dominant transport behavior can survive above 50 K. The robust surface states in our V doped single crystal systems provide an ideal platform to study the Dirac fermions and their interaction with other materials above 50 K. *Corresponding

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“…Furthermore, the surfaces and edges are readily available for surface probes, allowing detection and fundamental study of signatures of the topological superconducting state. Following recent theoretical predictions [15], an intrinsic QSH state was demonstrated in a monolayer (ML) of 1T'-WTe 2 [1][2][3][16][17][18]. WTe 2 is attractive for studying the QSH edge modes because it can be readily incorporated in van der Waals heterostructures and has shown quantized edge conductance up to 100 K [3].…”

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confidence: 97%

Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

et al. 2020

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The quantum spin Hall (QSH) state was recently demonstrated in monolayers of the transition metal dichalcogenide 1T'-WTe 2 and is characterized by a band gap in the two-dimensional (2D) interior and helical onedimensional (1D) edge states [1][2][3]. Inducing superconductivity in the helical edge states would result in a 1D topological superconductor, a highly sought-after state of matter [4]. In the present study, we use a novel dry-transfer flip technique to place atomically-thin layers of WTe 2 on a van der Waals superconductor, NbSe 2 . Using scanning tunneling microscopy and spectroscopy (STM/STS), we demonstrate atomically clean surfaces and interfaces and the presence of a proximity-induced superconducting gap in the WTe 2 for thicknesses from a monolayer up to 7 crystalline layers. At the edge of the WTe 2 monolayer, we show that the superconducting gap coexists with the characteristic spectroscopic signature of the QSH edge state. Taken together, these observations provide conclusive evidence for proximity-induced superconductivity in the QSH edge state in WTe 2 , a crucial step towards realizing 1D topological superconductivity and Majorana bound states in this van der Waals material platform.Contemporary interest in topological superconductors has been driven by potential applications of their gapless boundary excitations, which are thought to be emergent Majorana quasiparticles with non-abelian statistics [5][6][7][8]. One path toward topological superconductivity is to realize an intrinsic spinless p-wave superconductor [9]. A powerful alternative is by using a conventional s-wave superconductor to induce Cooper pairing in topologically non-trivial states via the superconducting proximity effect, resulting in an effective pwave pairing [10]. This approach has recently been employed to engineer 2D topological superconductivity in epitaxial three-dimensional topological insulator films grown on a superconducting substrate [11,12], and 1D topological superconductivity by proximitizing a 2D QSH system in buried epitaxial semiconductor quantum wells [13,14]. While such demonstrations mark important milestones, there are clear advantages for exploring topological superconductivity in the van der Waals material platform. Using layered 2D materials allows the 2D QSH edge to be proximitized in vertical heterostructures, circumventing the length restrictions of lateral proximity-effect geometries. Furthermore, the surfaces and edges are readily available for surface probes, allowing detection and fundamental study of signatures of the topological superconducting state. Following recent theoretical predictions [15], an intrinsic QSH state was demonstrated in a monolayer (ML) of 1T'-WTe 2 [1][2][3][16][17][18]. WTe 2 is attractive for studying the QSH edge modes because it can be readily incorporated in van der Waals heterostructures and has shown quantized edge conductance up to 100 K [3]. Furthermore, ML WTe 2 was recently also shown to host intrinsic superconducting behavior below ∼1 K when electrostatically g...

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Imaging quantum spin Hall edges in monolayer WTe ₂

Abstract: Real-space imaging reveals rich microscopic details of the quantum spin Hall edge conduction in monolayer WTe2.

Cited by 147 publications

References 32 publications

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Quantum oscillations of robust topological surface states up to 50 K in thick bulk-insulating topological insulator

Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

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Imaging quantum spin Hall edges in monolayer WTe 2

Abstract: Real-space imaging reveals rich microscopic details of the quantum spin Hall edge conduction in monolayer WTe2.

Cited by 147 publications

References 32 publications

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Influence of lattice termination on the edge states of the quantum spin Hall insulator monolayer 1T′−WTe2

Quantum oscillations of robust topological surface states up to 50 K in thick bulk-insulating topological insulator

Proximity-induced superconducting gap in the quantum spin Hall edge state of monolayer WTe2

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Imaging quantum spin Hall edges in monolayer WTe ₂