Author ORCID Identifier
Date of Award
Doctor of Philosophy (PhD)
Physics and Astronomy
This dissertation presents two distinct research studies. The first study focuses on the fractional quantum Hall effect (FQHE) observed in two-dimensional electron systems subjected to high transverse magnetic fields. Specifically, we investigate the interplay between Zeeman spin splitting and correlation energy in a GaAs/AlGaAs 2D electron system. By tuning the spin energy, we observe transitions in the quantized Hall effect, resulting in changes in both the resistivity minimum (ρxx) and the Hall resistance (Rxy). We also uncover a size dependence in the tilt angle interval for the vanishing of certain resistance minima, with observable shifts in . These findings highlight the competition and crossover between different spin polarized states and distinct FQHE phenomena.
The second study focuses on different methods of fabricating graphene devices, including exfoliation techniques such as dry transferring and creating heterostructures, as well as chemical vapor deposition (CVD). The main objective is to investigate the hysteresis effect in graphene devices. Graphene samples prepared using these methods often display p-type characteristics and significant hysteresis under ambient conditions. Current annealing has emerged as a promising in-situ approach for cleaning graphene samples. However, extended periods of current annealing may introduce defects in the underlying substrate. To address this concern, we examine the hysteresis behavior of a graphene Hall bar device before and after current annealing. The graphene sample, grown on copper foils via CVD, undergoes annealing with different current levels. Our experimental methodology involves studying electron/hole transport by cooling the sample from room temperature to 35 K while applying a back-gate bias. By analyzing the hysteresis characteristics, we obtain valuable insights into the impact of current annealing on the electrical properties of graphene.
These two studies contribute to our understanding of complex electronic phenomena and the behavior of graphene under different experimental conditions. The findings presented in this dissertation offer valuable insights into the underlying physics and practical considerations for these systems, paving the way for further research and potential technological applications.
Wijewardena, Udagamage, "Fractional Quantum Hall Effect Under Tilted Magnetic Fields in GaAs/AlGaAs Heterostructure Hall Bar Devices, and the Effect of Current Annealing in CVD Graphene Devices." Dissertation, Georgia State University, 2023.
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