EXPERIMENTAL INVESTIGATION OF THE PAIRING STATE OF HIGH-TEMPERATURE SUPERCONDUCTORS

To address the issue of the pairing state in high-temperature supercon ductors. four different experimental investigations have been carried out on a single high-quality, untwinned single crystal of LuBa2Cu3O7-d elta. These include measurements of the specific heat in magnetic fiel ds, both near the transition temperature and at low temperatures, inve stigations of the angular dependence of the transverse magnetic moment in the nonlinear Meissner regime, and the measurement of microwave pr operties leading to the temperature dependences of the penetration dep th and the surface resistance at low temperatures. Some of the results raise questions relating to the existence of a pairing state with lin e nodes in the energy gap, whereas others appear to be consistent with this picture. The results taken together suggest that studies of the pairing state be examined critically for possible alternative explanat ions.