Doctor of Philosophy (PhD)
First Advisor's Name
Grover L. Larkins
First Advisor's Committee Title
Second Advisor's Name
Jean H. Andrian
Second Advisor's Committee Title
Third Advisor's Name
John L. Volakis
Third Advisor's Committee Title
Fourth Advisor's Name
Fourth Advisor's Committee Title
Fifth Advisor's Name
Pete E. C. Markowitz
Fifth Advisor's Committee Title
Sixth Advisor's Name
Yuriy A. Vlasov
Sixth Advisor's Committee Title
Superconductivity, Superconductor, Graphene, Charge Carrier Transport, Nernst, BKT, 2D material, Vortex, Vortices, Magnetic
Date of Defense
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.
Sornkhampan, Nalat, "Study of Charge Carrier Transport in Graphene and Graphite as Two Dimensional and Quasi-Two Dimensional Materials and Their Interfaces" (2019). FIU Electronic Theses and Dissertations. 4019.
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