Reproducible tunneling determination of the electron--phonon spectral function in optimally-doped Bi-2212 single-crystal break junctions

Abstract

In this article we describe the reproducible determination of the electron density of states (DOS) of Bi 2Sr 2CaCu 2O 8+ x (BSCCO) we recently obtained by applying an unfolding procedure to the tunneling d I/d V data of break junctions made in single crystals with T c=93±2 K. The main result is the reproducible determination of the electron–phonon spectral function α 2( ω) F( ω) of BSCCO from seven different curves by using the standard program for the inversion of the Eliashberg equations (EE) and by taking into account an appropriate energy dependence of the normal DOS. The coupling constant λ, calculated consistently with the presence of the energy-dependent normal DOS, shows values between 1.9 and 2.7. The consequences of d-wave pair symmetry in the direct solution of the EE with reference to our experimental data are also discussed.