Contrasting impurity-induced magnetism and dynamics in 2H-MoTe2
We investigate the behavior of interstitial $^8$Li$^+$ implanted near the surface of 2H-MoTe$_2$ using $\beta$-detected NMR. We find that, unlike the muon, $^8$Li$^+$ does not show any signature of induced magnetism. This result is consistent with density functional theory, which identifies the Li stopping site at the 2a Wyckoff position in the van der Waals gap and confirms the absence of detectable Li-induced electronic spin polarization. Both the spin-lattice relaxation and the resonance lines show evidence of strong spin dynamics above $\sim 200$ K, reminiscent of local stochastic $^8$Li$^+$ motion within a cage. The resonance line shape consists of quadrupolar satellites on top of a broad central peak. To better understand the interaction of $^8$Li$^+$ with the host material, we employ a frequency-comb measurement, by simultaneously exciting four frequencies corresponding to the first-order quadrupolar satellite transitions, $\nu_0 \pm 3\nu_{\mathrm{comb}}$ and $\nu_0 \pm\nu_{\mathrm{comb}}$ around the Larmor frequency $\nu_0$ as a function of $\nu_{\mathrm{comb}}$. This offers an enhanced sensitivity to the quadrupolar split portion of the line. Using this method, we find a small decrease of the quadrupolar frequency with increasing temperature, showing the typical behavior associated with thermally excited phonons and the absence of any magnetic response which was observed with other defects in 2H-MoTe$_2$.