Resonant tunneling in high-T-c superconductors (review)

Papers are reviewed on the resonant tunneling mechanism of the c-axis trans port in high-temperature superconducting layered cuprates, proposed by the present author. After an introduction, where the problem is stated and the qualitative principles of the mechanism are described, real physical proper ties are calculated and compared with experimental data. These include the temperature dependence of the static c-axis conductivity in the normal stat e, frequency dependence of the optical conductivity and stationary supercur rent along the c-axis. It is demonstrated that for the latter the coherence of resonant tunneling through different centers is of primary importance. In the last section an explanation is proposed of the drastic decrease of T -c ad increase of the BCS ratio 2 Delta(0)/T-c with underdoping, based on t he disruption of interlayer connection and appearance of vortex fluctuation s. Two appendices are added illustrating some important features of resonan t tunneling on simple models. (C) 1999 Elsevier Science B.V. All rights res erved.