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Probing unconventional transport regimes in delafossite metals
|McGuinness, Philippa Helen
|xi, 164 p.
|This thesis describes investigations into the origins and nature of the remarkable electrical transport of the delafossite metals PtCoO₂ and PdCoO₂ using focused ion beam based microstructuring techniques. These compounds are amongst the highest conductivity materials known, but questions remain regarding the origin of their ultralow resistivity and the effects of their properties on transport in unconventional regimes such as the ballistic regime. In the initial introductory chapters, I will review the key properties of both delafossite metals and the application of focused ion beam microstructuring to transport measurements within This thesis describes investigations into the origins and nature of the remarkable electrical transport of the delafossite metals PtCoO₂ and PdCoO₂ using focused ion beam based microstructuring techniques. These compounds are amongst the highest conductivity materials known, but questions remain regarding the origin of their ultralow resistivity and the effects of their properties on transport in unconventional regimes such as the ballistic regime. In the initial introductory chapters, I will review the key properties of both delafossite metals and the application of focused ion beam microstructuring to transport measurements within low resistivity materials. The experimental findings are split into two chapters. Initially, I will describe an investigation into the origins of the high conductivity by introducing defects to PtCoO₂ and PdCoO₂ through high energy electron irradiation and observing the changes to the resistivity. These measurements demonstrate that the ultralow resistivity of the delafossite metals is the result of an extreme purity of up to 1 defect in 120,000 atoms, rather than backscattering suppression. In addition, I will report the effects of the defects on the electrical transport more broadly. Here, by examining the difference before and after irradiation, insight is gained into the origins of the unconventional magnetotransport of PtCoO₂. The other study uses PtCoO₂ and PdCoO₂ as test systems for the investigation of the effects of a non-circular Fermi surface on the transport within four terminal, square-shaped junctions inside the ballistic regime. These junction devices have been shown to be a sensitive probe of this regime in other materials, and I will demonstrate that the nearly hexagonal Fermi surface of the ultrapure delafossite metals results in not only strongly ballistic behaviour, present at a scale multiple times the mean free path, but also novel phenomena which are not seen with a circular Fermi surface.
|"I also acknowledge ﬁnancial support granted as a student of the Scottish Condensed Matter Centre for Doctoral Training under grant no. EP/L015110/1 from the Engineering and Physical Sciences Research Council and from the Max Planck Society. The electron irradiation studies were supported by the EMIR&A French network (FR CNRS 3618) at their SIRIUS facility." -- Acknowledgements
|University of St Andrews
|Data underpinning Philippa's Helen McGuinness thesis. McGuinness, P.H., University of St Andrews. DOI: https://doi.org/10.17630/f464e1b5-3f24-4ca8-bdca-180478f4b932
|Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
|Focused ion beam
|Non local transport
|Probing unconventional transport regimes in delafossite metals
|Engineering and Physical Sciences Research Council (EPSRC)
|Max-Planck-Gesellschaft zur Förderung der Wissenschaften
|PhD Doctor of Philosophy
|The University of St Andrews
|Thesis restricted in accordance with University regulations. Print and electronic copy restricted until 25th May 2023
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