Low Temperature Electrical Transport Behavior of AlOx / KTaO3 Based Two Dimensional Electron Gases

Krantz, Patrick Wallace

doi:https://doi.org/10.21985/n2-9m03-g583

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Low Temperature Electrical Transport Behavior of AlOx / KTaO3 Based Two Dimensional Electron Gases

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Necessity is the mother of innovation. In the wake of the pandemic, with no flow of samples and limited fabrication techniques available, necessity demanded a new material platform and adaptable methods to make complex oxide samples worth measuring. The material platform was KTaO3 , the younger successor to the mainstay of complex oxide work, SrTiO 3 , and the method was in-house aluminum evaporation that generated a conducting gas on the surface of the unassuming crystal squares. The result of this innovation was the conducting gas at the interface of the AlOx / KTaO3 heterostructure, fabricated into Hall bars to measure conducting properties and search for novel physics. KTaO 3 has previously been shown to host a number of interesting properties, including large spin orbit interactions due to the conducting 5d orbitals on the Ta atoms, superconductivity on the (110) and (111) crystal terminated faces up to 2 K, and a readily tunable set of conducting properties with an applied back gate voltage. These properties were confirmed in two sets of conducting samples fabricated as described, and showed improvement in both carrier concentration and carrier mobility compared to similar works in the literature. The samples also showed a series of novel results, in particular the emergence of macroscopic magnetism evident in hysteretic peaks observed in magnetotransport measurements. The second set of samples were fabricated in such a way to induce superconductivity, and those samples showed peaks in carrier concentration as a function of applied gate voltage, indicated the presence of a Lifshitz transition in the nature of the conduction. This unexpected carrier dependence on gate voltage was reflected in the superconducting properties, which showed other novelties including an upper gate limit to the superconductivity, a coexistence of the superconductivity with the macroscopic magnetism, and non-trivial relationship between carrier concentration and Tc , which is a strict departure from the literature. An analysis of the superconducting state followed, showing other peculiarities, and the work extends to measurements of the quantum nonlinear Hall effect which do not agree with theory for most of the samples investigated. In total, this work forms a broad basis for research on the novel transport properties of the AlO 3 / KTO interface, and suggests several experiments to dive deeper into unexplained results encountered along the way.

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