The pairing state of high temperature superconductors: Magnetic, thermal and microwave measurements on a single crystal

The pairing state has been studied through measurements of the transvers magnetic moment in the nonlinear Meissner regime. This investigation, which probes properties over a volume determine by the penetration depth, and is thus a bulk measurement, does not support a pure d-wave picture of the pairing state. The crystal on which much of the data has been obtained was subject to other experimental investigations which reveal it to be of a quality comparable to those of the best cuprate crystals in the YBCO family. These include measurements of the specific heat in magnetic fields, both near the transition temperature and at low temperatures, the measurement of microwave properties leading to the temperature dependences of the penetration depth and the surface resistance at low temperatures. Only the microwave measurements were unequivocally in agreement with the findings of others which have been interpreted as being supportive of d-wave pairing. This suggests that it is necessary to seek alternative explanations for some data interpreted within a d-wave framework.