Resonant tunneling in high-Tc superconductors

A review is presented of the author's work on resonance tunneling as an electron transport mechanism along the c axis in high-temperature layered cuprates. A formulation of the problem is given, qualitative aspects of the mechanism are described, and physical properties calculated. Comparisons are made with experimental data for the temperature dependence of normal conductivity, the frequency dependence of optical conductivity, and the stationary supercurrent along the c axis. For the latter, the resonance tunneling coherence of different centers is shown to be of crucial importance. Weakened interplane coupling and vortex fluctuations are invoked to explain the sharp drop in T_c and the rise in the 2Δ(0)/T_c ratio with decreasing oxygen content. Simple example models are given to demonstrate major aspects of resonance tunneling.