Evidence linking an oxygen pairing process and superconductivity in high temperature superconductors

Ultrasonic studies at 85 and 130 KHz about the Tc region of melt-textured Sm123 (SmBa2Cu3O7-δ), Y123, Nd123 and Bi2212 with a different structure, yielded details of strain amplitude dependent and time dependent phenomena. The results can be interpreted in terms of an oxygen related pairing process associated with a minor structural change in each of the high temperature superconductor materials. This pairing was evident for temperatures below Tc up to over 130 K and is thus linked to the phenomena of superconductivity. It has provided evidence for the pseudo-gap phenomenon as well as a possible mechanism that provides for channelling of superconducting carriers. An activation energy of ∼30 meV, in Y123, is associated with the pairing process. This is comparable with the thermal energy in the Tc region and indicates that the number of pairs decreases with increasing temperature, to an extent that superconductivity is basically suppressed, while the remnant pairs still contribute to the pseudo-gap phenomena