Tunneling spectroscopy of Tl2Ba2CaCu2O8 single crystals and thin films

Early electron tunneling experiments with the Tl2Ba2CaCu2O8 measured \Delta = 16-28 meV, while bulk optical experiments measured \Delta = 43-45 meV. We report new tunneling measurements of Tl2Ba2CaCu2O8 single crystals and c-axis oriented thin films, where the measured \Delta values on both sample types cover the range of 24-50 meV, with more than 70% of the junctions displaying \Delta > 30 meV. This work resolves the inconsistency between previously published results of tunneling and optical experiments. New tunneling conductances reveal improved superconducting gap region characteristics consistent with d-wave symmetry. The tunneling spectra also display features similar to the dip feature observed in Bi2Sr2CaCu2O8. We discuss our results in context of experiments reported previously on related materials.