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

We report $^{125}\mathrm{Te}$ NMR measurements of the topological quantum material ${\mathrm{ZrTe}}_{5}$. Spin-lattice relaxation results, well explained by a theoretical model of Dirac electron systems, reveal that the topological characteristic of ${\mathrm{ZrTe}}_{5}$ 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, ${T}_{c}=85$ K, in our crystals. We demonstrate that the changes in NMR shift at ${T}_{c}$ also provide direct evidence of band inversion when the topological phase transition occurs.

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