Pseudo gap, resonant tunneling and charge dynamics in cuprate superconductors

The pseudo gap of cuprate superconductors has often been related to a spin gap kT *. As an alternative kT * explanation the Coulomb gap Delta U * of blocking layer intermediate state tunneling is proposed, kT * congruent to Delta U * is presented as a function of doping and blocking layer width by the counteraction of overlap and charging energies with the tunnel barrier height phi(o) congruent to 2 eV, which also describes quantitatively the perpendicular transport in the normal and superconducting state, in addition, the states at E-F of the blocking layer with their Delta U *-values explain various spectroscopic observations ranging from specific heat to electron spectroscopy, like scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) sampling the blocking layer. For YBCO, quasi-localized holes in the blocking layer resonant with the extended CuO2 states are found essential for the superconducting interaction hinting to bosonic exchanges with the blocking layer as one possible cause for the superconducting coherence. (C) 1998 Elsevier Science B.V. All rights reserved.