Fig. 3. Resistivity and lnρ versus T^{−1/ν + 1} plots of Li_xFe₇Se₈.

(A) The resistivities for two different Li doping samples (0.53 and 0.89) and parent compound (Fe₇Se₈) are shown from 2 to 300 K. Overall, the metallic Fe₇Se₈ is turned into insulators by doping electrons. The measurements are performed roughly on ab plane. Above x = 0.53, the slope of resistivity is negative (dρ/dt < 0), indicating an insulating behavior. This nonmetal behavior is enhanced with increasing the Li doping. (B) Plots of lnρ versus T^−1/ν+1 of Li_0.89Fe₇Se₈ from 2 to 10 K. We fit the same resistivity data of Li_0.89Fe₇Se₈ by using VRH formulas ρ = ρ₀·exp(T₀/T)^1/(ν+1), where ν = 1, 2, and 3 corresponding to 1D, 2D, and 3D material, respectively. ν = 0, which denotes the traditional insulator with band gap, is also included for comparison. ν = 3 fits best among all the fittings.