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

Ultrasonic studies at 85 and 130 KHz about the T_c region of melt-textured Sm123 (SmBa₂Cu₃O_7-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 T_c 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 T_c 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.