Contrasting impurity-induced magnetism and dynamics in 2H-MoTe2

TL;DR

This study uses $eta$-detected NMR to explore impurity-induced magnetism and spin dynamics in 2H-MoTe$_2$, revealing no induced magnetism from $^8$Li$^+$ and identifying strong spin fluctuations above 200 K.

Contribution

It demonstrates that $^8$Li$^+$ does not induce magnetism in 2H-MoTe$_2$, contrasting with muon results, and introduces a frequency-comb NMR technique to analyze quadrupolar interactions with enhanced sensitivity.

Findings

No detectable Li-induced electronic spin polarization.

Strong spin dynamics observed above 200 K.

Quadrupolar frequency decreases with temperature, indicating phonon interactions.

Abstract

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$_2$.