Magnetic-Field-Tuned Quantum Phase Transitions Exhibited by Indium Oxide

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Magnetic-Field-Tuned Quantum Phase Transitions Exhibited by Indium Oxide

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2021-07

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The magnetic-field-tuned quantum superconductor-insulator transitions of disordered amorphous indium oxide films are a paradigm in the study of quantum phase transitions, and exhibit power-law scaling behavior. The properties of these films can be tuned by varying the carrier concentration and disorder by adjusting the oxygen partial pressure during deposition or by annealing after deposition. These films are known to undergo disorder, magnetic field, and charge carrier density-tuned transitions, most commonly superconductor-insulator transitions. A pair of indium oxide films exhibiting an unconventional superconductor-metal transition will be discussed in this dissertation along with the noise properties of a film exhibiting a more conventional transition. For superconducting indium oxide films with low disorder, such as the ones reported on in Chapter 4, the high-field state appears to be a quantum-corrected metal. Resistance data across the superconductor-metal transition in these films are shown here to obey an activated scaling form appropriate to a quantum phase transition controlled by an infinite randomness fixed point in the universality class of the random transverse-field Ising model. Collapse of the field-dependent resistance vs. temperature data is obtained using an activated scaling form appropriate to this universality class, using values determined through a modified form of power-law scaling analysis. This exotic behavior of films exhibiting a superconductor-metal transition is caused by the dissipative dynamics of superconducting rare regions immersed in a metallic matrix, as predicted by a recent renormalization group theory. The smeared crossing points of isotherms observed are due to corrections to scaling which are expected near an infinite randomness critical point, where the inverse disorder strength acts as an irrelevant scaling variable. For superconducting indium oxide films with higher disorder, a more conventional superconductor-insulator transition is observed. Low frequency resistance measurements performed on such a film are shown in this dissertation. Contrary to initial expectations there were no significant changes in the noise properties near the quantum critical point. However, it was found that the noise varied in a way that was consistent with predictions based on a percolation model. Specifically, the noise properties suggest that the superconductor-insulator transition can be modeled by p-model percolation. This model is based on random Josephson junction array models which have been used extensively to explain the properties of granular superconductors.

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University of Minnesota Ph.D. dissertation. July 2021. Major: Physics. Advisor: Allen Goldman. 1 computer file (PDF); vii, 174 pages.

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Lewellyn, Nicholas. (2021). Magnetic-Field-Tuned Quantum Phase Transitions Exhibited by Indium Oxide. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/225027.

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