Dirac electron behavior and NMR evidence for topological band inversion in ZrTe5

We report 125Te NMR measurements of the topological quantum material ZrTe5. Spin-lattice relaxation results, well explained by a theoretical model of Dirac electron systems, reveal that the topological characteristic of ZrTe5 is T dependent, changing from weak topological insulator to strong topological insulator as temperature increases. Electronic structure calculations confirm this ordering, the reverse of what has been proposed. NMR results demonstrate a gapless Dirac semimetal state occurring at a Lifshitz transition temperature, Tc=85 K, in our crystals. We demonstrate that the changes in NMR shift at Tc also provide direct evidence of band inversion when the topological phase transition occurs