Tunneling spectrum indicating phonon contribution to high T _c oxide superconductivity

Abstract

Improved tunneling spectroscopy with [BSCCO(2212)/SiO _x ]/Au tip point contact junction enables us to observe significant peaks in the tunneling conductance derivative spectrum$\frac{{d^2 I}}{{d^2 V}} - V$. Their peak energy eV _i could be systematically assigued byeV _i −Δ = ηε₀ +ħω _i (ph) withn=0,1,2. Here,ħω _i means each phonon mode energy and ε₀ = 72meV was found just corresponding to the breathing mode of the Cu−O bond stretching in the CuO₂ plane, which indicates that these characteristic optical phonons play an essential role in the high T _c superconductivity. The infrared reflectance spectrum by Capizzi et al. on similar substance is found in peak correspondence.