Twistable electronics with dynamically rotatable heterostructures

Abstract

The electronic properties of two-dimensional materials and their heterostructures can be dramatically altered by varying the relative angle between the layers. This makes it theoretically possible to realize a new class of twistable electronics in which device properties can be manipulated on-demand by simply rotating the structure. Here, we demonstrate a new device architecture in which a layered heterostructure can be dynamically twisted, in situ. We study graphene encapsulated by boron nitride where at small rotation angles the device characteristics are dominated by coupling to a large wavelength Moiré superlattice. The ability to investigate arbitrary rotation angle in a single device reveals new features in the optical, mechanical and electronic response in this system. Our results establish the capability to fabricate twistable electronic devices with dynamically tunable properties.The weak van der Walls forces between the atomic planes in 2D materials makes it possible to fabricate devices with arbitrary rotational order. This provides a new opportunity in device design where electronic properties are controlled by varying the relative twist angle between layers [1]. Indeed several studies have established that in heterostructures assembled from 2D crystals, electron tunneling between layers varies strongly with rotation [2][3][4][5][6][7][8]. In twisted bilayer graphene (two monolayers in direct contact but with an angle mismatch between the layers) several novel phenomenon have been predicted and observed, including topological valley transport [9-13], and superconductivity [14], as a consequence of angledependent interlayer coupling. Likewise, the formation of interlayer excitons in transition metal dichalcogenide heterostructures is highly sensitive to angle [15][16][17].The effect of rotational alignment between conducting and insulating 2D layers can be equally significant. A remarkable example is provided by graphene coupled to hexagonal boron nitride (BN). Owing to the closely matched lattice constants a large Moiré superlattice develops near zero angle mismatch [18,19]. This substantially alters the graphene band structure opening an energy gap at the charge neutrality point (CNP) and creating replica Dirac points at higher energies [20][21][22].Several techniques have been developed to fabricate layered heterostructures with controlled rotation between the layers, including optical alignment of crystal edges [18,[20][21][22], rotational alignment [23] during assembly, and self-alignment through thermal annealing [24,25]). However, in each case a priori understanding of the crystallographic orientation of each layer is required before assembly; motion between the layers during assembly makes it difficult to achieve precise angle control; and most significantly, once assembled the angle can not be further modified. Here, we present a new experimental technique that provides on-demand control of the orientation between layers in a van der Waals heterostructure. We study a BN/graphene/BN structure w...

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