Optical and Infrared Properties

One of the most important features in the IR region of the spectrum should be the appearance of the superconducting energy gap. The higher transition temperature materials should display larger values for the gap if they are BCS superconductors. The gap observed for BaPbj.jjBijPg has been shown to agree with the BCS prediction (57). 

Raman spectra indicate that phonons are coupled to electronic states in BaPb BijPj (53) and in Ba1.xKxBiOs (58). These studies do show a strong electron - phonon interaction is present in the superconducting phases, but do not prove that these modes are responsible for high Tc driven by a phonon - only mechanism. 

Tunneling Spectroscopy has revealed electron - phonon coupling strengths for optical phonons in Ba K BiOg which suggest that phonon mediated coupling is responsible for superconductivity in this system (59). 

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