Correlating electrical transport properties of twisted bilayer graphene with the structure of its moiré

A rich collection of electronic phases has been observed in twisted van der Waals moirés. Yet systematic study of these phases has been limited by inability to precisely set the interlayer twist between layers, and by microscopic differences in the structure of the moiré which can lead samples of nominally the same twist angle to behave differently. I will discuss our attempts to correlate the underlying moiré structure with the resultant electronic properties. Moiré structure is typically inferred from electrical transport measurements, which reveal only the average unit cell area, not strain which is known to alter the electronic properties. We fill in this structural information gap by using torsional force microscopy to directly map moirés prior to completing encapsulation of the heterostructure. From these moiré maps we characterize the twist angle and strain, and their uniformity over microns. We then fabricate devices carefully aligned to the mapped regions, and conduct electrical transport measurements.