Theory of photoemission line shape in high-temperature superconductor Bi2Sr2CaCu2O8+δ via dipolon mediated electron-electron pairing mechanism

Hitherto unexplained experimentally observed photoemission line shape near (π, 0) in superconductor Bi2Sr2CaCu2O8+δ characterized by a peak followed at high energy by a dip and a broad feature has been explained here naturally by dipolon mediated electron-electron pairing mechanism of high-Tc superconductors. In the superconducting state the peak is formed by excitation solely of a quasiparticle whereas the broad feature is formed by the excitation of a quasiparticle with concomitant excitation of a dipolon for coupling with the process of creating a photoelectron. In the normal state the photoemission spectra observed in the underdoped, optimally doped and overdoped samples are due to the excitations of O1,1 and O1,2 dipolons. The theory predicts the possibility of observing dipolon side bands in photoemission spectra in superconducting state in favorable conditions. We deduce that the dipolon theory provides not only explanation for the observed kink but predicts also the existence of new weak kinks in single-quasiparticle energy dispersion.