Modeling of Eliashberg Spectral Functions for HIGH-Tc Superconductors

The Eliashberg spectral density function has been constructed using the phonon density of states obtained from INS experiments. In doing so we have used a simplified but more realistic form for α²F(ω) and also avoided the elaborate process of numerically solving the Eliashberg equations. The resulting spectral functions for several high-T_c superconductors (e.g., LSCO, YBCO and BSCCO) with the easy use of available expressions reproduce the observed critical temperature, gap ratio and several other parameters. T_c is found to increase with λ (electron-phonon coupling constant) in such a manner that it is much stronger than those obtained from several equations, constructed from numerical solution of the Eliashberg equations for lower λ values. The obtained functions show widely spreading spectra that inhibit lattice instability by yielding not too large values of λ (<2.95).