Determination of the tunneling electron-phonon spectral function in high-Tc superconductors with energy dependence of the normal density of states

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Abstract
We discuss the limits and the correct utilization of the standard program for the inversion of Eliashberg equations and the determination of the electron-phonon spectral function and the coulomb pseudopotential from tunneling measurements in high-Tc superconductors. In order to compare the calculated density of states with the experimental one, we introduce the results of the inversion procedure, applied to our recent tunneling data in Bi2Sr2CaCu2O{8+x} (BSCCO) single-crystal break junctions with Tc=93 K, in a direct program for the solution of Eliashberg equations. Most of the observed differences between theoretical and experimental curves at energy greater than gap can be explained by a smooth energy dependence of the normal density of states that we introduced in the direct solution of the Eliashberg equations. The electron-phonon coupling constant determined in a self-consistent way is equal to 2.69, giving evidence for a strong electron-phonon interaction in BSCCO. Similar results have been obtained in 7 break-junction tunneling curves measured on the same BSCCO single crystals.

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