ABSTRACTSuperconducting Ba0.6K0.4BiO3, with a Tc of 30K, shows a large 18O isotope effect which indicates that phonons are involved in the pairing mechanism. Infrared reflectivity measurements indicate a value for the superconducting gap consistent with moderate coupling (2Δ/kTc = 3.5 ± 0.5). A mediating energy for pairing of about 40 meV would be required to obtain a Tc of 30K. Strong coupling of electrons by optical phonons (which are present in this material with energies up to 80 meV) could account for the observed transition temperature. Recent tunneling spectroscopy shows the presence of strongly coupled optical phonons in the 40 to 70 meV region, indicating that superconductivity in this material may be phonon mediated.
Break-junction tunneling spectroscopy for doped semiconductors in the hopping regime