Mitchell Institute for Fundamental Physics & Astronomy
College Station, Texas 77843
Much of my talk will focus on our results for the topological quantum material **ZrTe_5**. Long studied as a candidate for charge-density wave transformations, layered ZrTe5 has recently been recognized as a Dirac electron system. Its behavior includes a topological phase transition joining two different massive Dirac regimes, although there have been a number of conflicting reports about the nature of this transformation. NMR spectroscopy provides a local probe of the fluctuating Dirac carriers, and we have used this to provide a quantitative measure of the T-induced gap separating the Dirac cones. Combined with DFT-based electronic structure calculations, we also showed that the transition involves a change from weak to strong topological insulator as temperature increases, the reverse of what had been proposed. Given the tunability and 2D nature of this material, these properties may lend themselves to new quantum electronic applications. Finally, I will also discuss our recent results on half-Heusler type semiconductor materials, including signatures of the topological inversion from trivial to inverted-band configuration in Bi-based superconducting materials.