Manipulating anisotropic transport and superconductivity by focused ion beam microstructuring
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This thesis presents the results of electrical transport experiments performed on two microstructured quantum materials, namely on the ultra-pure metal PdCoO₂ and on the heavy fermion superconductor CeIrIn₅. Throughout this work, focused ion beam (FIB) microsculpting was utilised to design the investigated devices. I begin with an introduction to the FIB instrument, with a specific focus on its application for microstructuring transport devices from quantum materials. In particular, our standard fabrication procedure, in which a thin slab of material is extracted from a bulk single crystal for further processing is described in detail, as this approach can be utilised for most metallic compounds. Furthermore, I describe a micro-fabrication process for creating transport devices from platelet-shaped single crystals. Thereafter I present ballistic transport measurements of the ultra-pure delafossite metal PdCoO₂. By investigating mesoscopic transport bars which are narrower than the electron mean free path (up to 20 μm), I demonstrate that the ballistic transport in PdCoO₂ is strongly anisotropic as a result of the underlying quasi-hexagonal Fermi surface shape. Moreover, I report on the results of transverse electron focusing (TEF) experiments, a technique which directly probes the real space ballistic trajectories of electrons in a magnetic field, which demonstrate the super-geometric focusing effect. Furthermore, by investigating microstructures of the superconducting heavy fermion compound CeIrIn₅ by means of transport measurements as well as scanning SQUID microscopy in collaboration with external groups, a route to controllably manipulate the local strain in microstructured devices was found. The presented approach is based on exploiting the substrate-induced biaxial strain due to differential thermal contraction, which is spatially tailored by defined FIB cuts. As the superconducting transition in the heavy fermion compound CeIrIn₅ is highly sensitive to strain, the local T[sub]c within the device is controlled via the spatial strain distribution.
Thesis, PhD Doctor of Philosophy
Attribution-NonCommercial-NoDerivatives 4.0 Internationalhttp://creativecommons.org/licenses/by-nc-nd/4.0/
Embargo Date: 2021-06-03
Embargo Reason: Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 3rd June 2021
Description of related resourcesManipulating anisotropic transport and superconductivity by focused ion beam microstructuring (Thesis data) Bachmann, M.J., University of St Andrews. DOI: https://doi.org/10.17630/38c95513-b893-4cc6-8f91-529100888e58
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