Josephson current in Hybrid Semiconductor-Superconductor One-Dimensional devicesZhang, Bomin (2023) Josephson current in Hybrid Semiconductor-Superconductor One-Dimensional devices. Doctoral Dissertation, University of Pittsburgh. (Unpublished) This is the latest version of this item.
AbstractSuperconducting and semiconducting materials have been extensively studied as separate topics within the field of condensed matter, significantly contributing to the scientific and technological advancements of the 21st century. The hybrid systems combining these advancements have emerged as the primary focus in mesoscopic physics and quantum technology. While superconducting qubits based on these systems have demonstrated their superiority, topologically protected Majorana qubits hold considerable potential for future fault-tolerant quantum computing. However, the realization of Majorana zero modes (MZM) requires the elegant balancing of various effects, including spin-orbit interaction, proximity-induced superconductivity, gate tuning, and Zeeman splitting, and it is crucial to have a profound understanding of these physics within microscopic devices. In this thesis, the primary focus is on the Josephson effect in hybrid nanowires junctions, using DC Josephson current as a tool to study spin-orbital interaction and orbital effect. We first present our recent progress in Sn shell formation on InSb nanowires. Material analysis reveals a uniformly smooth shell half-covering the InSb nanowires and well-separated superconductor islands. Transport results indicate strong proximity-induced superconductivity. The enhanced proximity effect expands the parameter space into new regimes, suppressing disorder in the system and forming the basis of our studies in nanowire Josephson junctions. Our studies of the Josephson effect proceed in two directions. On the one hand, we focus on fine-tuning transverse modes to achieve supercurrent transport through a single conduction channel. The orbital effect in the presence of an external field is analyzed by comparing the decay rate of supercurrent in few and multi-mode scenarios. On the other hand, we explore the skewed diffraction pattern of supercurrent induced by spin-orbit interaction, demonstrating that it is a $\phi_0$-junction with higher-order harmonics. These three studies collectively illustrate our progress in reducing disorder in the system and exploring orbital and spin-orbit effects in nanowire junctions—crucial steps toward realizing MZM in hybrid systems. In the final chapter, we study InSb nanowires coated with CdTe shells. Morphological studies reveal epitaxial growth of CdTe with a uniform thickness and a defect-free interface. This structure may inspire the design of future hybrid devices for realizing MZMs. Share
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