Probing electron-electron and electron-phonon interactions in twisted bilayer graphene

Abstract

Two-dimensional systems, and, most recently, moire systems, have risen to the forefront of condensed matter physics with the advent of experimental techniques that allow for controlled stacking of van der Waals heterostructures [17, 54]. For example, it was recently discovered that when two pieces of atomically thin carbon (graphene) are twisted at 1.1° with respect to one another, they display a variety of effects, including superconducting behavior [10]. Experimental investigation of the behavior of small-angle twisted bilayer graphene (SA-TBG) as a function of twist angle is imperative to understanding the mechanisms that play into the many interesting, strongly-interacting phenomena that the moire system displays. In this thesis, I present three experiments which explore electron-electron and electron-phonon interactions in SA-TBG. I first consider SA-TBG as a host for a viscous electron fluid and look for the onset of fluid behavior via electron transport. Then I investigate the temperature dependence of resistivity in SA-TBG devices at a number of angles. The final experiment examines magnetophonons in three devices above the magic angle and compares the findings to theoretical results.