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Two-dimensional quantum electronics with a twist

Matthew Yankowitz, Columbia University
Monday, February 4, 2019 - 4:00pm
PAA 102

A wide family of atomically-thin van der Waals (vdW) materials can be mixed and matched as desired to fabricate heterostructures without the usual interfacial constraints of conventional crystal growth, providing a simple path towards realizing on-demand designer electronics. These additionally host fundamentally new degrees of freedom such as the twist angle between neighboring crystals, which controls emergent moiré superlattice potentials that modify the band structure and overall device properties. I will discuss a number of recent experiments characterizing and controlling the electronic properties of various twisted vdW heterostructures. As a prototypical example, graphene encapsulated between boron nitride (BN) exhibits a sizable band gap when the crystals are well-aligned. I will discuss methods to directly tune this band gap by controllably aligning either one or both of the BN layers to the graphene, or by modifying the strength of the interlayer electronic coupling with pressure. I will also discuss bilayers of graphene, in which superconductivity and correlated insulating phases emerge for twist angles of ~1.1°. In a device with 1.27° twist angle – in which correlated phases are otherwise absent – application of pressure drives emergent superconductivity with record-high Tc of over 3 K.

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