Edge conduction in monolayer WTe2

• Published in: Nature physics Vol. 13; no. 7; pp. 677 - 682
• Main Authors: Fei, Zaiyao, Palomaki, Tauno, Wu, Sanfeng, Zhao, Wenjin, Cai, Xinghan, Sun, Bosong, Nguyen, Paul, Finney, Joseph, Xu, Xiaodong, Cobden, David H.
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.07.2017; Nature Publishing Group; Nature Publishing Group (NPG)
• Subjects: 140/133; 142/126; 639/766/119/2792; 639/766/119/995; Atomic; Backscattering; Bilayers; Boundary layer; Classical and Continuum Physics; Complex Systems; Condensed Matter Physics; Cooling; Elastic scattering; Electric contacts; Electric potential; Hall effect; letter; Low temperature; Magnetic fields; Mathematical and Computational Physics; Molecular; Monolayers; Optical and Plasma Physics; Physics; Quantum Hall effect; Quantum physics; Resistance; Theoretical; Topological insulators; Topology
• ISSN: 1745-2473; 1745-2481
• DOI: 10.1038/nphys4091

Experiments showing that a single layer of WTe 2 can conduct electricity along its edges while insulating in the interior suggests that this material is a two-dimensional topological insulator. A two-dimensional topological insulator (2DTI) is guaranteed to have a helical one-dimensional edge mode 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 , 11 in which spin is locked to momentum, producing the quantum spin Hall effect and prohibiting elastic backscattering at zero magnetic field. No monolayer material has yet been shown to be a 2DTI, but recently the Weyl semimetal WTe 2 was predicted 12 to become a 2DTI in monolayer form if a bulk gap opens. Here, we report that, at temperatures below about 100 K, monolayer WTe 2 does become insulating in its interior, while the edges still conduct. The edge conduction is strongly suppressed by an in-plane magnetic field and is independent of gate voltage, save for mesoscopic fluctuations that grow on cooling due to a zero-bias anomaly, which reduces the linear-response conductance. Bilayer WTe 2 also becomes insulating at low temperatures but does not show edge conduction. Many of these observations are consistent with monolayer WTe 2 being a 2DTI. However, the low-temperature edge conductance, for contacts spacings down to 150 nm, never reaches values higher than ∼20 μS, about half the predicted value of e 2 / h , suggesting significant elastic scattering in the edge.