Magnetotransport at charge neutrality in graphene-based devices

The Dirac point of graphene has been the subject of intense study for the past two decades. Unusual properties arise owing to its linearly vanishing density of states, along with the high mobility of thermally excited charge carriers. Studying the Dirac point in ultra-high quality graphene samples enables investigations of its nature with minimal complications from charge disorder. Here, we will discuss several unusual magnetotransport features of the charge neutrality point in different graphene-based devices, including monolayer and Bernal bilayer graphene as well as various graphene double-layer structures. Under suitable conditions, we see unexpected negative longitudinal magnetoresistance at cryogenic temperatures. As the temperature is raised, there are additional anomalies in a magnetic field in both the longitudinal and Hall resistivities. We will discuss possible origins of these observations, including semiclassical effects and electron-hole drag mechanisms mediated by Coulomb interactions.