Resonant tunneling in high-Tc superconductors (review)

Papers are reviewed on the resonant tunneling mechanism of the c-axis transport 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 properties are calculated and compared with experimental data. These include the temperature dependence of the static c-axis conductivity in the normal state, frequency dependence of the optical conductivity and stationary supercurrent 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 the disruption of interlayer connection and appearance of vortex fluctuations. Two appendices are added illustrating some important features of resonant tunneling on simple models. (C) 1999 Elsevier Science B.V. All rights reserved.