Evolution of the resistivity anisotropy in Bi2Sr2-xLaxCuO6+δ single crystals for a wide range of hole doping -: art. no. 104512

To elucidate how the temperature dependence of the resistivity anisotropy of the cuprate superconductors changes with hole doping, both the in-plane and the out-of-plane resistivities (rho(ab) and rho(c)) are measured in a series of high-quality Bi2Sr2-xLaxCuO6+delta (BSLCO) single crystals for a wide range of x (0.23less than or equal toxless than or equal to1.02), which corresponds to the hole doping per Cu, p, of 0.03-0.18. The anisotropy ratio, rho(c)/rho(ab), shows a systematic increase with decreasing p at moderate temperatures, except for the most underdoped composition where the localization effect enhances rho(ab) and thus lowers rho(c)/rho(ab). The exact p dependence of rho(c)/rho(ab) at a fixed temperature is found to be quite peculiar, which is discussed to be due to the effect of the pseudogap that causes rho(c)/rho(ab) to be increasingly more enhanced as p is reduced. The pseudogap also causes a rapid growth of rho(c)/rho(ab) with decreasing temperature, and, as a result, the rho(c)/rho(ab) value almost reaches 10(6) in underdoped samples just above T-c. Furthermore, it is found that the temperature dependence of rho(c) of underdoped samples show two distinct temperature regions in the pseudogap phase, which suggests that the divergence of rho(c) below the pseudogap temperature is governed by two different mechanisms.