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

TL;DR

This paper analyzes the electron-phonon spectral function in high-Tc superconductor BSCCO using tunneling data and Eliashberg equations, revealing strong electron-phonon coupling and the importance of energy-dependent density of states.

Contribution

It introduces a method to incorporate energy dependence of the normal density of states in the inversion of tunneling data for high-Tc superconductors.

Findings

Electron-phonon coupling constant is 2.69, indicating strong interaction.

Energy dependence of the density of states explains discrepancies at energies above the gap.

Consistent results obtained from multiple tunneling measurements.

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.