Exploring Topology and Electronic Correlations in Square-Net Materials – A High-Field Study

In this thesis detailed quantum oscillation (QO) studies have been performed on two different van der Waals layered, square-net material systems, i.e., the Dirac nodal line (DNL) semimetals ZrSiS, HfSiS, and ZrSiSe, all members of the ZrSiS material family, and CeTe3, a member of the rare-earth tritellurides (RETe3). All the experimental work has been carried out at the High Field Magnet Laboratory & FELIX Laboratory (HFML-FELIX), Radboud University, Nijmegen, the Netherlands. The high magnetic fields enabled us to fully determine the Fermi surface (FS) of the three ZrSiS material family members by studying QOs in the de Haas-van Alphen (dHvA) and the Shubnikov-de Haas (SdH) effect. We stress that it is very unique to determine the topology of the FS in such complex quantum materials. The observation of magnetic breakdown (MB) and quantum interference (QI) phenomena further aided in the full determination of the FS and opens up the way to investigate MB theory in topological material systems. For CeTe3 the high magnetic fields enabled us to extend the known magnetic phase diagram and observe electronic correlations in the form of enhanced cyclotron masses due to interactions between the antiferromagnetic and electronic ground states. In doing so we have provided a basis to understand the bulk electronic properties in topological and correlated material systems which will enable future investigations to study the evolution of the electronic properties by applying uniaxial strain, hydrostatic pressure, as well as the fabrication of thin films and monolayers by mechanical exfoliation.本论文针对两类范德瓦尔斯层状方格网材料体系开展了详尽的量子振荡（quantum oscillation, QO）研究，其一为隶属于ZrSiS材料家族的狄拉克节线（Dirac nodal line, DNL）半金属ZrSiS、HfSiS与ZrSiSe，其二为稀土三碲化物（rare-earth tritellurides, RETe3）家族成员CeTe3。全部实验工作均在荷兰奈梅亨拉德堡德大学的高场磁体实验室与FELIX实验室（HFML-FELIX）中完成。借助强磁场环境，我们通过研究德哈斯-范阿尔芬（de Haas-van Alphen, dHvA）效应与舒布尼科夫-德哈斯（Shubnikov-de Haas, SdH）效应中的量子振荡信号，完整确定了ZrSiS家族三种材料的费米面（Fermi surface, FS）拓扑结构。需特别强调，在这类复杂量子材料中确定费米面的拓扑结构极具特殊性。磁击穿（magnetic breakdown, MB）与量子干涉（quantum interference, QI）现象的观测，进一步辅助完成了费米面的完整解析，并为在拓扑材料体系中研究磁击穿理论开辟了新路径。针对CeTe3，强磁场帮助我们拓展了已知的磁相图，并观测到由反铁磁基态与电子基态之间的相互作用所引发的、以回旋质量增强形式体现的电子关联效应。本研究为理解拓扑与关联材料体系中的体相电子性质奠定了基础，可为后续通过施加单轴应变、静水压，以及通过机械剥离制备薄膜与单层材料，探究电子性质的演化规律提供支撑。