IVANOV A.S.

Peter the Great St. Petersburg Polytechnic University, St. Petersburg, Russia
Institute Laue-Langevin, Grenoble, France

 Spectra of magnetic and lattice excitations  in high-temperature superconductors

Spectra of lattice vibrations and magnetic fluctuations in several families of copper- and iron-based high-temperature superconductors have been measured by inelastic neutron scattering. It is found that ionic coupling is dominating in cuprates with vibrations screened by free electrons when injected as a function of composition. Effects of electron-phonon interaction are present but not pronounced. Low energy magnetic excitations in antiferromagnetic stoichiometric cuprates with symmetric (tetragonal) crystal structures are described by introducing short-range pseudo-dipolar interactions. Magnetic resonance excitation (spin resonance) is shown to be of universal nature in the superconducting state of different families of new superconducting materials. The resonance spectral weight is described using an itinerant electron model with a superconducting gap of particular symmetry different from that of conventional superconductors with electron-phonon interaction mechanism.