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Observation of Time-Reversal Invariant Helical Edge-Modes in Bilayer Graphene/WSe2Heterostructure

Tiwari, P and Srivastav, SK and Ray, S and Das, T and Bid, A (2021) Observation of Time-Reversal Invariant Helical Edge-Modes in Bilayer Graphene/WSe2Heterostructure. In: ACS Nano, 15 (1). pp. 916-922.

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Official URL: https://dx.doi.org/10.1021/acsnano.0c07524


Topological insulators, along with Chern insulators and quantum Hall insulator phases, are considered as paradigms for symmetry protected topological phases of matter. This article reports the experimental realization of the time-reversal invariant helical edge-modes in bilayer graphene/monolayer WSe2-based heterostructures - a phase generally considered as a precursor to the field of generic topological insulators. Our observation of this elusive phase depended crucially on our ability to create mesoscopic devices comprising both a moiré superlattice potential and strong spin-orbit coupling; this resulted in materials whose electronic band structure could be tuned from trivial to topological by an external displacement field. We find that the topological phase is characterized by a bulk bandgap and by helical edge-modes with electrical conductance quantized exactly to 2e2/h in zero external magnetic field. We put the helical edge-modes on firm ground through supporting experiments, including the verification of predictions of the Landauer-Büttiker model for quantum transport in multiterminal mesoscopic devices. Our nonlocal transport properties measurements show that the helical edge-modes are dissipationless and equilibrate at the contact probes. We achieved the tunability of the different topological phases with electric and magnetic fields, which allowed us to achieve topological phase transitions between trivial and multiple, distinct topological phases. We also present results of a theoretical study of a realistic model which, in addition to replicating our experimental results, explains the origin of the topological insulating bulk and helical edge-modes. Our experimental and theoretical results establish a viable route to realizing the time-reversal invariant Z2 topological phase of matter. © 2020 American Chemical Society.

Item Type: Journal Article
Publication: ACS Nano
Publisher: American Chemical Society
Additional Information: The copyright of this article belongs to American Chemical Society
Keywords: Electric insulators; Graphene; Magnetic fields; Quantum chemistry; Quantum theory; Spin orbit coupling; Superconducting materials, Displacement field; Electric and magnetic fields; Electrical conductance; Electronic band structure; Experimental realizations; External magnetic field; Mesoscopic devices; Topological phasis, Topology
Department/Centre: Division of Physical & Mathematical Sciences > Physics
Date Deposited: 25 Feb 2021 10:54
Last Modified: 25 Feb 2021 10:54
URI: http://eprints.iisc.ac.in/id/eprint/68048

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