Topological van der Waals metamaterials
Abstract
Title: Topological van der Waals metamaterialsCombining dissimilar materials can lead to composite structures with physical properties notfound in the constituents and device functionalities not found in natural materials. In the electronicdomain, heterostructuring can be used to create tunable electronic devices with novel properties.This YIP proposal will use van der Waals heterostructuring to create topological metamaterialstwo dimensional devices whose electronic performance is protected from material imperfectionsby the underlying structure of the electron wave functions.We seek to extend uses of topological protection beyond the quantum Hall effect to high temperaturesand zero magnetic field. We focus on two related effects. The quantum anomalousHall (QAH) effect hosts chiral edge states arising from magnetic ordering, generating a quantizedHall effect at zero magnetic field. Besides providing a low-cost resistance standard, quantumanomalous Hall systems may provide novel mechanisms for magnetoelectric coupling, with applicationsin low power memory and spintronics. The quantum spin Hall (QSH) effect instead hostshelical edges, with counter-propagating modes protected from scattering by time-reversal symmetry.QSH insulators form the basis for applications ranging from dissipationless interconnects totopologically-protected quantum bits.Despite the promise of topology as a conceptual underpinning for two dimensional electronicdevices at zero magnetic field, to date the known physical realizations provide, at best, proofsof concept which fail to perform as expected by theory. In the case of the quantum anomalousHall effect, for example, conventional approaches are limited to realizing the effect at sub-kelvintemperature scales, several orders of magnitude below the magnetic ordering temperatures. Forquantum spin Hall systems, electrons propagate less than a micron before backscattering.The proposed work will develop new, robust realizations of these phenomena using van derWaals heterostructureslayered stacks of two dimensional crystals fabricated by aligned transferof atomically thin crystals. Van der Waals heterostructures afford novel control knobs for electronicstructure, including digital control over chemically incompatible atomic layers and controlover interlayer twist angle to tune interlayer coupling. The proposal will build on the developedcapabilities of the PIs lab to fabricate complex van derWaals heterostructures of exceptional quality.Under an ONR YIP award the PI will introduce the additional ingredients for higher temperaturetopological states via two interrelated thrusts:Thrust 1: New topological phases from van der Waals proximity effects. This thrust willengineer high-quality topological phases using interlayer coupling in heterostructures of grapheneand transition metal compounds. Targets include QSH in rhombohedral trilayer and twisted bilayergraphene proximal to WSe2, and QAH in heterostructures of graphene and antiferromagnetictransition metal thiophosphates.Thrust 2: Higher temperature orbital magnetism via moire engineering. This thrust willseek new, higher temperature platforms for orbital magnetism driven QAH states, particularly multilayermoire heterostructures including twisted tri- and four-layer graphene and moire-patternedrhombohedral graphite surface states, both of which may host exceptionally flat bands with finiteChern number.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 20, 2020
- Source ID
- N000142012609
Entities
People
- Andrea Young
Organizations
- Office of Naval Research
- United States Navy
- University of California, Santa Barbara