Anisotropic polarons in lightly doped La 2CuO 4

The unusual anisotropy of an activation energy for the conductivity of highly pure La ₂CuO ₄ is explained in terms of disk-like polarons with large in-plane radius and small interplane one. For such a polaron the anisotropy of the mobility mechanism appears in a wide range of T: the in-plane hops are thermoactivated, while the interplane ones are due to the quantum tunneling. The T-dependence of Hall effect and the possibilities for the microscopic structure of a polaron in La ₂CuO ₄ are briefly discussed.