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Recently discover topological semimetals exhibit a wealth of interesting behavior due to the presence of massless Dirac and Weyl fermions, and the associated topologically-enforced interface and boundary states. Such states include the surface Fermi arcs identified in Weyl and Dirac systems, and “drumhead” surface states of more extended nodal-line topological semimetals, with high density of topological surface states of interest for possible emergent topological surface superconductivity. These materials can also be driven into the quantum limit in relatively small magnetic fields, offering new platforms for studying interacting Fermi systems in a field-enforced reduced dimensionality. I will discuss our recent work on several quasi-2 dimensional topological semimetals, focusing especially on ZrSiTe and ZrTe5, with nuclear magnetic resonance providing a highly effective probe of the conducting states in these systems. ZrSiTe features a symmetry protected Dirac nodal-line, in which massless electron-hole states extend along a line, rather than at a single point, in momentum space. One result of our work is the demonstration that the nodal-line configuration of ZrSiTe leads to a 2-dimensional van Hove singularity in the density of states, a log singularity that could make this an interesting host for an anomalous superconducting transformation. ZrTe5 has a single Dirac node and it has emerged as a fertile system for the exploration of quantum-limit behavior, and in this limit one result I will discuss is our demonstration of a field-induced transformation that we identify with a mass-generation connected to the appearance of an exciton insulator state in this system.

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