Resonant ionic bonding and high TC superconductivity

The implications of an electronic coupling model in high TC superconductors of YBCO are discussed in which the pairing mechanism is based upon the ionic bonding. Specifically,the bonding reaction Cu + O [rlhar2] Cu-- resonates at a frequency of I2πh̵; in the CuO planes, where I = 0.4 eV is the ionic bonding energy. We formulate an Hamiltonian which allows for the reduction of the total energy by I each time two holes or two electrons form a pair. The total energy consists of kinetic energy calculable from band theory, and the ionic bonding energy proportional to I. We calculate (i) the effective Ginzburg-Landau free energy for all T < Tc, (ii) the energy gap, (iii) the anisotropic London penetration depths, and (iv) the anisotropic coherence lengths. General agreement is found between our calculations and experimental data.