Tunneling effects in highly anisotropic layered superconductors

A brief review of the galvanomagnetic properties of highly anisotropic cuprate superconductors is presented, with an emphasis on the internal Josephson effect, which naturally exists in multilayer HTSC crystals. The transport of charge carriers perpendicular to the layers in such materials occurs by successive tunneling of quasiparticles (or Cooper pairs) between highly conducting (or superconducting) $\rm {CuO_2}$ layers through intermediate buffer layers. Currently available results on the nonmetallic conductivity along the $c$-axis in the normal state are analyzed, as are data on the distinctive branched current-voltage characteristics in the superconducting state, which are clear experimental manifestations of tunneling effects in layered cuprate superconductors.