Abstract
This thesis explores the fundamental properties and behaviors of novel superconductors and topological materials through a combination of experimental techniques and theoretical analyses.
Chapter 1 provides an overview of the thesis scope, motivation, and organization.
Chapter 2 establishes the theoretical framework for superconductivity, covering the history, basic phenomena, and the development of key theories, including London theory, Ginzburg–Landau theory, BCS theory, Green’s function representations, and the Eliashberg framework. The chapter also discusses the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state, an exotic superconducting phase that can emerge under high magnetic fields.
Chapter 3 shifts focus to the experimental techniques used in this study. Resistance as a function of temperature, DC magnetization, AC susceptibility, specific heat, and pointcontact spectroscopy are the key methods for probing the properties of superconductors and topological materials.
Chapter 4 presents a detailed investigation of the Sb2Te3/Fe1+yTe heterostructure. This includes the structural properties, electrical transport measurements, and point-contact spectroscopy results, with particular emphasis on the roles of spin–orbit coupling, interfacial superconductivity, and Sb2Te3 thickness in the observed superconducting behavior.
Chapter 5 examines the isotropic superconductor Ti4Ir2O. The chapter covers magnetization experiments, specific heat measurements, and the construction of the H–T phase diagram, followed by a detailed analysis of the point-contact spectroscopy data, which provides insights into the superconducting gap structure of Ti4Ir2O.
Chapter 6 explores superconductivity-like behavior in ultrathin boron-doped carbon nanotube networks confined in zeolite (CNT@ZSM-5). Across multiple batches, magnetization shows an onset of Meissner-like diamagnetism in the 220–250 K range, accompanied by ZFC/FC splitting, while specific heat exhibits a small anomaly near 230 K that broadens and weakens under an applied magnetic field. Transport measurements show a transition-like resistance drop in the same 220 K window and a strong dependence on compression. Point-contact spectroscopy further reveals gap-like conductance features that weaken with temperature and become indistinguishable above 230 K. AC susceptibility shows a steplike feature in χ’(T) and a spike-like feature in χ”(T)around 220 K at ambient pressure, and also shows a pressure dependence consistent with the interpretation drawn from the resistance measurements.
Finally, Chapter 7 concludes the thesis with a summary of the key findings and their implications for understanding unusual superconductivity and topological materials. The appendix provides the relevant codes used for curve fitting.