On the electronic and magnetic excitation spectra of high-T-c Cu oxides inthe normal and superconducting states

In the discussion of the electronic excitation of high T-c Cu oxides, effec ts of the energy broadening of the quasi particles have to be considered. I f it is properly done, data of the tunneling density of states published fo r Bi2Sr2CaCu2O8+delta system can provide a clear indication that the pseudo gap observed above T-c can naturally be understood as the precursor of the superconducting gap. The broadening has been taken into account in simple calculations of the magnetic excitation spectra chi " (q, omega) of YBa2Cu3 Oy, with a model which is essentially based on the band picture and include s the exchange coupling among electrons. By comparing the calculated result s with observed data, experimental evidence for the quasi particle broadeni ng has been found. Brief arguments are presented if the picture of the dyna mical "stripes" which affect the superconductivity works in YBa2Cu3Oy.