One of the still very much disputed questions is the origin of the superconducting pairing in the high-Tc cuprate superconductors. We have studied exchange of spin fluctuations as a possible mechanism of high-Tc superconductivity. The advantage of this mechanism is that it naturally leads to d-wave superconductivity and is able to provide high values of Tc [4]. Analyzing experimental data on the spin excitation spectrum from inelastic neutron scattering we could show that this mechanism provides more energy than is necessary for superconductivity [3]. In a collaboration with the neutron scattering group of Bernhard Keimer at the Max-Planck-Institute for Solid State Research in Stuttgart and the photoemission group of Sergey Borisenko at the IFW in Dresden we used the spin excitation spectrum to calculate photoemission spectra and compare them with experimental data on the same single crystals [2]. The result of this work was that the major structures seen in the spin excitation spectrum and the photoemission spectra can be related to each other. In particular, the neutron resonance can be related to the photoemission peak-dip-hump structure and the photoemission "kink" can be related to the upper branch of the neutron hourglass dispersion (see picture). Calculation of the superconducting properties leads to a d-wave superconducting state with a high value of Tc. These results strongly suggest that the main driving force in the high-Tc cuprate superconductors is based on magnetic interactions.
