Novel transport regimes in graphene

Abstract

Transport phenomena in solids -- such as energy and charge flows in response to external fields -- is a subject of fundamental interest for solid state physics. Carrier transport exhibits a wide variety of intriguing and potentially useful behaviors arising due to a rich and complex interplay between electron-disorder, electron-electron, and electron-phonon interactions. Graphene, a newly discovered carbon one-atom-thick material, has unique transport characteristics, some of which are already well understood, whereas some are being under investigation or are waiting to be discovered. The two-dimensional character and exceptional cleanness of graphene, as well as gate tunability of the carrier density and electron-electron interactions, make graphene an excellent platform to study a range of new transport regimes, such as quantum-coherent ballistic transport, electron hydrodynamics and energy dissipation at the atomic scale. We will study ballistic transport in the context of electronic lensing. We will also demonstrate that electron-electron scattering alters ballistic transport in a dramatic way, giving rise to hole backflows and "memory effects", and leading to experimental signatures such as negative non-local resistance. Upon further increase of the electron-electron interaction strength, the system enters the hydrodynamic regime, where a host of new phenomena can emerge. We also show that the electron-disorder interactions have important implications for energy transport, with energy dissipation occurring predominantly at atomic-scale defects. In this thesis, we will provide a detailed discussion of these topics and their connection to the ongoing experiments.