Three-dimensional superconductivity induced by an extremely small amount of Li in LixSnSe2

Unconventional superconductivity occurs often in materials with low dimensionality. Here, we report superconductivity observed in layered LiₓSnSe₂ with the superconducting transition temperature Tc~6 K. Through Li⁺ intercalation in semiconducting SnSe₂ via electrochemical process, LiₓSnSe₂ is formed with an extremely small x value as estimated from the c-axis lattice parameter, carrier concentration, and first-principles calculations. Electrical resistivity and magnetic susceptibility measurements allow the construction of both lower (Hc1ᵃᵇ) and upper critical field (Hc2ᵃᵇ4pt0exand4pt0exHc2ᶜ) phase diagrams. While Hc2ᶜ obtained from 10% and 50% resistivity drops exhibits linear temperature dependence, Hc2ᶜ4pt0ex(90%4pt0exresistivity4pt0exdrop), Hc1ᵃᵇ, and Hc2ᵃᵇ can be described by the empirical formula Hci(T)=Hci(0)[1-(TTc0)²] ($i=1$, 2), giving Hc2ᶜ(0)=754 Oe, Hc1ᵃᵇ(0) = 27 Oe, and Hc2ᵃᵇ(0) = 1652 Oe. Using the Ginzburg-Landau formula, we further estimate that the c-axis penetration depth λc(0) = 396 nm and the coherence length anisotropy ξab(0) = 66.1 nm and ξc(0) = 30.3 nm. The fact that ξc(0) is much longer than the interlayer separation implies three-dimensional superconductivity with superconducting anisotropy ξab(0)/ξc(0) {~} 2.2.