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.