Anisotropy of the critical current density in a layered electron-doped superconductor Nd2–xCexCuO4+δ

The results of studying the conductivity and critical current density in monocrystalline Nd2–xCexCuO4+δ/SrTiO3 (x = 0.15; 0.17) films with c-axis perpendicular or parallel to the substrate plane are presented. It is found that in stoichiometrically annealed films with the optimum cerium content (x = 0.15) the resistance anisotropy is maximal and the anisotropy of the critical current density is jcab/jcc ≅ 3 · 103 at T = 4.2 K. The strong anisotropy of the critical current density is considered in the framework of natural superlattices, with alternating conductive CuO2 and non-conducting buffer Nd(Ce)O layers. It is shown that the high density of the critical current along the conductive CuO2 planes is caused by the pinning of vortices on the buffer layers, whereas the strong anisotropy of the critical current is caused by the anisotropic motion of the vortex lattice in the layered superconductor.