Study of Charge Carrier Transport in Graphene and Graphite as Two Dimensional and Quasi-Two Dimensional Materials and Their Interfaces
Evidence of superconductivity in phosphorous-doped graphite and graphene has been observed at temperatures in the vicinity of 260 K. This evidence includes transport current, magnetic susceptibility, Hall and Nernst measurements. All of these measurements indicate a transition of a type II superconductor without a phase of type I until below the limits of the measurement capabilities. Vortex states are inferred from periodically repeated steps in the R vs. T characteristics of Highly Oriented Pyrolytic Graphite and exfoliated doped multilayer graphene. The presence of vortices has been confirmed with thermal gradient driven Nernst measurements. Magnetic susceptibility measurements have shown results qualitatively similar to those expected (and experimentally observed by others) for ultra-thin films (thickness << the London penetration depth). The magnetic susceptibility is negative for field-cooled and zero-field-cooled measurements. The susceptibility for field-cooled and zero-field-cooled measurements begin to diverge at approximately 260 K. Hall effect measurements show a sign reversal in the Hall voltage as the temperature is reduced from 300 K to 78 K. The Nernst effect confirms a Berezinskii-Kosterlitz-Thouless (BKT) vortex transition at T~ 40 K and several pinned vortices’ melting temperatures which correlate with the resistive measurements. Finally, in completeness, we have observed a charge BKT transition at T~ 4 K in both susceptibility and resistive measurements, and a vortex BKT transition in both the resistive, Nernst, and susceptibility measurements at T~ 40 K.
Electrical engineering|Computer Engineering|Physics
Sornkhampan, Nalat, "Study of Charge Carrier Transport in Graphene and Graphite as Two Dimensional and Quasi-Two Dimensional Materials and Their Interfaces" (2019). ProQuest ETD Collection for FIU. AAI28151299.