Date of Award
Doctor of Philosophy (PhD)
We report a study on the phenomenon of extraordinary magnetoresistance (EMR) in boron nitride encapsulated monolayer graphene devices. Extremely large EMR values–calculated as the change in magnetoresistance, (R(B)–R0)/R0–can be found in these devices due to the vanishingly small resistance values at zero field. In many devices the zero-field resistance can become negative, which enables R0 to be chosen arbitrarily close to zero depending only on measurement precision, resulting in very large EMR. We critically discuss the dependence of EMR on measurement precision and device asymmetry. On the other hand, we also find the largest reported values of the sensitivity to magnetic fields, given by the derivative dR/dB. Moreover, the sensitivity measured in a two-probe configuration is over an order of magnitude larger than in the standard four-probe configuration. Additionally, the gate-voltage-dependent resistance at zero field shows a strong electron-hole asymmetry, which we trace to the nature of the metal-graphene edge contact: as in the well-studied case of metals deposited on graphene, the graphene at one-dimensional edge contacts also appears to be heavily electron-doped leading to the appearance of a resistive pn junction in the neighborhood of the central metallic shunt, when the bulk of graphene is gated to be p-type. We also report the effects of the sizes of the devices and the ratios of metallic disk to graphene on the EMR.
Chair and Committee
Ken Kelton, Chuan Wang, Li Yang, Kater Murch,
Zhou, Bowen, "Extraordinary Magnetoresistance in Encapsulated Graphene Devices" (2019). Arts & Sciences Electronic Theses and Dissertations. 1801.