  Creating carrier reservoirs in layered compounds can effectively tune the
carrier density, which often induces a variety of emergent properties. Based on
solid-ion-conductor gating technique, we successfully induce superconductivity
of 4.8 K in ultrathin Li-intercalated SnSe2 samples. The Li+ ions are driven in
between interspacing of SnSe2 layers and form a single reservoir layer to
provide electrons. In addition, a dome-like T c is found through substituting
of S for Se, where the optimal T c is 6.2 K for SnSe1.8S0.2. Density functional
theory calculations confirm that the intercalated LiSnSe2 is thermodynamically
favorable, where the intercalation of Li expands the interlayer spacing by 10%
and increases the carrier density by two orders of magnitude. Meanwhile the
calculated results reveal that the enhanced electron-phonon interaction due to
softened phonon determines the occurrence of superconductivity. Our results
demonstrate that this strategy is very effective to explore superconductors in
layered materials with narrow bandgap.
