CVD-based graphene twistronics

Twisted bilayer graphene (TBG) is certainly the major driving force of the novel paradigm of twistronics, which aspires at understanding and engineering the emergent electronic properties of twisted two-dimensional (2D) materials. The main tool used so far to fabricate TBG is the dry assembly of mechanically exfoliated flakes, combined with the tear-and-stack technique. However, the use of exfoliated graphene presents limits in terms of future perspective, scalability and realistic applications. In this thesis work, we demonstrate that graphene bilayer twistronics can be effectively realized by adopting graphene single crystals synthesized with a scalable approach, i.e., chemical vapor deposition (CVD). Either by direct growth or by tailored assembly we fabricate TBG, both in the regimes of large and small twist angle, and we study the electronic properties of these twisted systems via (magneto)transport, spectroscopic and microscopic measurements. First, we demonstrate that large-area 30◦-rotated bilayer graphene (30-TBG) can be deterministically obtained at the growth stage, ensuring electronic decoupling and parallel transport between pristine graphene sheets with a gatecontrolled carrier distribution. This results in simultaneous ultrahigh mobility and conductivity, unattainable in a single layer of graphene. Based on the parallel transport mechanism, we then introduce a method for in situ measurements of the chemical potential of the two layers. The extent of information obtained has the potential to greatly simplify the measurement of thermodynamic quantities in graphene-based systems of high current interest. In the second part of the thesis we present a tailored approach to realize high-quality TBG in the small-angle regime (SA-TBG) starting from separated CVD-grown graphene single crystals. Via low-temperature magnetotransport measurements on a dual-gated device we populate the moiré bands of a 2.4◦-TBG beyond the van Hove singularities, showing tunability between different regimes of interlayer coupling. Besides multiple gate-tunable Landau fans, we observe moiré-induced features, which unambiguously support the achievement of interface cleanness and device-scale twist-angle uniformity. The effectiveness of the assembly approach in obtaining twist angles close to the magic angle (MA) and below it is also demonstrated via scanning probe techniques and (magneto)transport data. The realization of twisted bilayer systems with scalable CVD graphene displaying sharp interfaces and peculiar magnetotransport features is a first step towards the realization of large-scale twisted systems, which will not only accellerate fundamental studies but also expand the perspective applicative potential of these enticing systems. The demonstration of large-scale highquality hBN (or alternative suitable dielectrics) and of viable solutions to obtain twist angle control over large areas are two central challenges that will need to be addressed and overcome in order to fully realize scalable CVD graphene-based twistronics.