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Abstract
Topographic corrugations, such as wrinkles, are known to introduce diverse physical phenomena that can significantly modify the electrical, optical and chemical properties of two-dimensional materials. This range of assets can be expanded even further when the crystal lattices of the walls of the wrinkle are aligned and form a superlattice, thereby creating a high aspect ratio analogue of a twisted bilayer or multilayer – the so-called twisted wrinkle. Here we present an experimental proof that such twisted wrinkles exist in graphene monolayers on the scale of several micrometres. Combining atomic force microscopy and Raman spectral mapping using a wide range of visible excitation energies, we show that the wrinkles are extremely narrow and their Raman spectra exhibit all the characteristic features of twisted bilayer or multilayer graphene. In light of a recent breakthrough – the superconductivity of a magic-angle graphene bilayer, the collapsed wrinkles represent naturally occurring systems with tuneable collective regimes.
Highlights
A twist between the individual layers of a graphene bilayer enables the observation of new phenomena, such as superconductivity or Mott insulating states, which are unknown for single layer graphene[1]
Twisted bilayer graphene with the misorientation angle in a suitable range can be conveniently identified using Raman spectroscopy, as superlattice-activated Raman processes give rise to two new Raman modes: RTO and RLO4,7,8, where the subscripts refer to the respective phonon branches
The activated wave vector is dependent on the actual misfit angle θ; the misfit angle can be determined from the measured Raman shift of the RTO and RLO modes
Summary
A twist between the individual layers of a graphene bilayer enables the observation of new phenomena, such as superconductivity or Mott insulating states, which are unknown for single layer graphene[1]. In some cases, it can be expected that both walls of the graphene wrinkle will be oriented in such a way that they form a collapsed wrinkle consisting of a twisted bilayer, if standing, which we call a ‘twisted
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