Quantum Tunneling of 7Li Spins in Argyrodite-Type Solids

The irregular movement of atoms or ions, known as self-diffusion, is a widespread phenom-enon in solids. In crystalline Li6.6P0.4Ge0.6S5I, the triplet arrangements within the Li-rich cag-es allow for ultrafast localized Li+ exchange processes. This feature leads us to consider whether, in addition to classical over-barrier hopping, quantum effects — commonly ob-served for electrons, protons, and deuterons — should also be taken into account for the heavier 7Li nuclei. To explore this hypothesis, we investigated 7Li spin fluctuations using nu-clear magnetic resonance (NMR) spin-lattice relaxation (SLR) measurements at cryogenic temperatures, down to T = 9 K. Our findings reveal signatures in the SLR NMR data that we attribute to (coherent) quantum tunneling of the Li spins within the triplet arrangement. These insights not only enhance our understanding of atomic jump processes but also sug-gest potential future quantum applications involving 7(6)Li+ tunneling.