NMR Investigation of the WTe₂ Weyl Semimetal below the Topological Transition Temperature

Abstract: NMR investigations are performed on ¹²⁵Te nuclei of WTe₂ Weyl topological semimetal at temperatures of 41 and 293 K. The measurements were carried out using a Bruker Avance 500 NMR pulse spectrometer. The ¹²⁵Te NMR spectra for a WTe₂ single crystal are obtained for the orientation of crystal axis c parallel and perpendicular to the quantizing field. A complicated form of the spectra was related to the presence of four nonequivalent positions of tellurium atoms in the crystalline structure of WTe₂. The longitudinal magnetization recovery was studied after the pulse saturation for particular spectral lines. An exponential character of relaxation is revealed. The frequency shift and width of spectral lines were found to be insignificantly different at the two temperatures, while the times of nuclear spin-lattice relaxation at 41 K exceeded approximately by 30 times the corresponding times measured at room temperature. The strong temperature dependence of the relaxation is supposedly related to the contribution of the Weyl quasi-particles below the topological phase transition.