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Title:The effects of disorder on superconducting islands and island arrays
Author(s):Garrido Menacho, Rita C.
Director of Research:Mason, Nadya
Doctoral Committee Chair(s):Van Harlingen, Dale J
Doctoral Committee Member(s):Phillips, Philip W; Stack, John D
Department / Program:Physics
Degree Granting Institution:University of Illinois at Urbana-Champaign
2D superconductivity
Josephson junction arrays
Granular superconductivity
Confined geometries
Quantum phase transitions
Vortex effects
Phase fluctuations
Abstract:Characterizing the role of disorder in 2D and mesoscopic superconducting materials has proven pivotal in the understanding of quantum phase transitions. In the presence of Anderson localization, electronic wavefunctions are known to become localized leading to strongly correlated phases of matter in which competing mechanisms including localization, Cooper pairing and interactions are at play. These strong interactions have been known to lead to unusual ground states and previously theoretically prohibited metallic states. However, despite various excellent theoretical and experimental efforts, the origin of these exotic ground states in the presence of disorder remains widely debated. Thus, controlling and tuning disorder has proven necessary to gain insights into the microscopic nature of superconductivity in the quantum regime. As a result, the work in this thesis lies in the intersection between superconductivity and disorder and focuses on (1) systematically characterizing the effects of disorder in the presence of thermal and magnetic field effects and (2) defining and tuning disorder parameters in a controllable and reproducible manner. We studied two different superconducting systems: single and coupled Nb islands as well as Sn island arrays on graphene. The Nb islands provided a way to study the effects of granularity (a form of disorder) on the onset of superconductivity of mesoscopic systems. We found the onset of superconductivity in these devices to be consistent with the formation of rare-regions. Moreover, in the presence of a magnetic field, these Nb islands presented an enhanced competition between vortex pinning effects and vortex-vortex interactions due to their confined geometry and strong disorder. The Sn island arrays on graphene served as a platform to study the effects of point disorder on the magnetic field-driven superconductor-insulator quantum phase transition. By tuning point disorder in the system, we observed an evolution of critical exponents and a crossover from a possible vortex glass to a likely Griffiths-type phase to a percolative-driven transition for devices having resistances less than the quantum of resistance R_Q.
Issue Date:2020-12-03
Rights Information:Copyright 2020 Rita Garrido Menacho
Date Available in IDEALS:2021-03-05
Date Deposited:2020-12

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