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

Abstract

We report 125 Te 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.

Optical conductivity and resistivity in a four-band model for ZrTe5 from ab initio calculations

“…Moreover, its position shifts with the filling, and therefore the chemical potential. This confirms theoretically the conclusions of key experiments which attributed the origin of the resistivity peak to the large shift of the chemical potential with temperature [7,[21][22][23]29,30]. In particular, we obtain this resistivity peak without relying on a topological phase transition.…”

“…Moreover, we find that μ varies strongly with temperature, to the point that between 0 and 300 K it sweeps an energy window larger than the gap. This matches ARPES measurements showing a large drop of μ when raising temperature [7,[21][22][23], as well as NMR results [30]. In addition, it is consistent with reports of strong variation of the carrier density with temperature in optical conductivity [10] and Hall [49] measurements.…”

“…The peak height increases with the gap from 0.5 m • cm for M 0 = 3 meV to 0.8 m • cm for M 0 = 33 meV. Experimental results show resistivity peaks at temperatures ranging from 60 K to 160 K whose maximum varies between 0.8 and 3 m • cm [9,10,12,17,[20][21][22]24,29,30,49] with which our results are consistent. Note that the peak height depends on γ : a larger value for γ would decrease the height of the Drude peak and therefore increase the resistivity.…”

“…The temperature of the resistivity maximum varied with sample thickness and doping [25][26][27]. Recently, this resistivity peak was also related to the potential topological properties of ZrTe 5 and interpreted as a signature for a transition upon cooling [28] from a WTI to an STI state [29] or the reverse [30], as well as a signature of Dirac polarons [31].…”

NMR determination of Van Hove singularity and Lifshitz transitions in the nodal-line semimetal ZrSiTe

“…This mechanism includes a significant contribution from carriers far from the nucleus without relying on local hyperfine fields. Evidence for this mechanism has been seen recently in other zirconium tellurides [34,35]. For a quasi-2D nodal line, one obtains (T 1 T ) −1 a = (3/2)(T 1 T ) −1 c [33], close to what is observed at low T (Fig.…”