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Molecular beam epitaxy and magnetotransport studies of thin films of the topological semimetal cadmium arsenide


Cd3As2 is a three-dimensional Dirac semimetal. Electrons in Cd3As2 behave like massless particles known as Dirac fermions. Their linear dispersion in momentum space results in novel properties, such as ultrahigh electron mobility, giant magnetoresistance, and chiral currents, among many others. Additionally, due to non-trivial topology of their electronic band structure, Cd3As2 has distinct surface and bulk electronic states.

In this dissertation, the epitaxial growth of Cd3As2 and its structural and electrical characterization are presented. Cd3As2 was synthesized by molecular beam epitaxy (MBE) which is a low energy deposition technique that enables the growth of high-quality thin films. First, I discuss the epitaxial growth of Cd3As2 in the theoretically predicted Dirac semimetal phase at low temperatures. Magnetotransport studies of quantum confined and biaxially strained Cd3As2 films showed transport signatures from robust two-dimensional surface states while the bulk electronic states were gapped out. Further, we explored the effect of dislocations on the carrier mobilities of the bulk and surface electronic states. Misfit dislocations were found to have little influence on the bulk carrier mobilities. In the next part of the study, we developed the growth of a capping layer by migration enhanced epitaxy to protect the surface states. In the last part, we discuss the anisotropic magnetoresistance and planar Hall effect in the Cd3As2 films as a combined effect of three mechanisms: the chiral anomaly, Berry phase, and orbital magnetoresistance.

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