Doctor of Philosophy (PhD)
Electrical and Computer Engineering
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Phosphorus-doped graphene, Mixed-state superconductivity, High-temperature superconductivity, Hysteresis
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Evidence of superconducting vortices, and consequently mixed-state superconductivity, has been observed in phosphorus-doped graphene at temperatures as high as 260 K. The evidence includes transport measurements in the form of resistance versus temperature curves, and magnetic measurements in the form of susceptibility and magnetic Nernst effect measurements. The drops in resistance, periodic steps in resistance, the appearance of Nernst peaks and hysteresis all point to phosphorus-doped graphene having a broad resistive region due to flux flow as well as a Berezinskii-Kosterlitz-Thouless (BKT) transition at lower temperatures.
The observation of irreversible behavior in phosphorus-doped graphene under the influence of a thermal gradient and an orthogonal applied magnetic field is a direct sign of mixed-state superconductivity, as it demonstrates the presence of vortices. The observations are based on cyclic Nernst measurements that show clear hysteresis that diminishes as the sample is warmed to temperatures higher than 200 K; voltage steps and anomalous structures related to field screening are observed at temperatures below 70 K; and finally, smaller Nernst peaks are seen at temperatures near 230 K pointing to vortex stacks having a high depinning and thermal energies.
Previously Published In
Sornkhampan N., Gil-Pinzon J., Ponce-Zuniga J., Woods A., Vlasov Y., Larkins G., (2021). Evidence of vortices and mixed-state superconductivity in phosphorus-doped graphene. Part I (Nernst). Superconductor Science and Technology 34 035022
Gil-Pinzon J., Sornkhampan N., Woods A., Vlasov Y., Larkins G., (2021). Evidence of vortices and mixed-state superconductivity in phosphorus-doped graphene. Part II (Hysteresis). Superconductor Science and Technology 34 03502
K. Holland, "Doping as a Possible Means to create Superconductivity in Graphene," 2016.
N. Sornkhampan, "Study of Charge Carrier Transport in Graphene and Graphite as Two Dimensional and Quasi-Two Dimensional Materials and Their Interfaces," 2019.
Gil Pinzon, Julian E., "A Study of Magnetism and Possible Mixed-State Superconductivity in Phosphorus-Doped Graphene" (2021). FIU Electronic Theses and Dissertations. 4744.
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