We propose a microscopic theory of the `$c$'-axis and in-plane transport of copper oxides based on the bipolaron theory and the Boltzmann kinetics. The fundamental relationship between the anisotropy and the spin susceptibility is derived, $\rho_{ c}(T,x)/\rho_{ ab}(T,x)\sim x/\sqrt{ T}\chi_{ s}(T,x)$. The temperature $(T)$ and doping $(x)$ dependence of the in-plane, $\rho_{ ab}$ and out-of-plane, $\rho_{ c}$ resistivity and the spin susceptibility, $\chi_{ s}$ are found in a remarkable agreement with the experimental data in underdoped, optimally and overdoped $La_{ 2-x}Sr_{ x}CuO_{ 4}$ for the entire temperature regime from $T_{ c}$ up to $800K$. The normal state gap is explained and its doping and temperature dependence is clarified.
Categories: cond-mat