ON THE INFLUENCE OF STRUCTURAL INSTABILITIES ON SUPERCONDUCTIVITY IN THE FRAMEWORK OF THE ELECTRON-PHONON MECHANISM

A model for the coupling of an anharmonic optical phonon branch, producing a structural phase transition at T = T0, with an electron band has been treated within the Eliashberg theory. The features of the model are discussed in relation to the HTSC-system La2-xSrxCuO4. The superconducting transition temperature Tc has its maximum value if the lattice is most unstable (Tc = T0). In general the calculated isotope effect differs significantly from the BCS-value due to lattice anharmonicity, even zero or negative values are possible. © 1990.