c-axis transport and resistivity anisotropy of lightly to moderately doped La2-xSrxCuO4 single crystals:: Implications on the charge transport mechanism -: art. no. 214535

Both in-plane and out-of-plane resistivities (rho(ab) and rho(c)) are measured in high-quality La2-xSrxCuO4 single crystals in the lightly to moderately doped region 0.01less than or equal toxless than or equal to0.10, and the resistivity anisotropy is determined. In all the samples studied, the anisotropy ratio rho(c)/rho(ab) quickly increases with decreasing temperature, although in nonsuperconducting samples the strong localization effect causes rho(c)/rho(ab) to decrease at low temperatures. Most notably, it is found that rho(c)/rho(ab) at moderate temperatures (100-300 K) is almost completely independent of doping in the nonsuperconducting regime (0.01less than or equal toxless than or equal to0.05); this indicates that the same charge confinement mechanism that renormalizes the c-axis hopping rate is at work down to x=0.01. It is discussed that this striking x independence of rho(c)/rho(ab) is consistent with the idea that holes form a self-organized network of hole-rich regions, which also explains the unusually metallic in-plane transport of the holes in the lightly doped region. Furthermore, the data for x>0.05 suggest that the emergence of the superconductivity is related to an increase in the c-axis coupling.