Quasi-two-dimensional transport properties of the layered superconductor Nd2−xCe x CuO4+δ

Abstract

The temperature dependences of resistivities ρab in the ab plane and ρc along the c axis have been studied for single-crystal Nd2 − x CexCuO4 + δ (x = 0.12, 0.15, 0.17, 0.20) films with (001) and (1\(\bar 1\)0) orientations. The superconducting transition temperature and anisotropy coefficient are shown to be maximal in optimally annealed samples (the oxygen content is close to the stoichiometric content, δ → 0). A combination of the metallic behavior of the ρab(T) dependence and the nonmetallic behavior of the ρc(T) dependence for the optimally annealed samples is an intrinsic property of the substance and an indication of the fact that the system is quasi-two-dimensional. This layered quasi-two-dimensional system is an Anderson dielectric with a strongly anisotropic localization radius (R loc ab ≫ R loc c ). An increase in the oxygen content and, hence, in the degree of disorder in the Nd2 − x CexCuO4 + δ system is found to decrease the resistivity anisotropy coefficient. Thus, a disorder-induced Anderson transition takes place in this quasi-two-dimensional system.