Intrinsic features of Bi2Sr2CaCu2O8+δ tunneling spectra: Scaling and symmetry of the energy gap

Tunneling measurements have been made on a series of high-quality Bi2Sr2CaCu2O8+δ (BSCCO) single crystals with transition temperatures (Tc) ranging from 79 to 92 K. From these systematic studies it has been possible to delineate the intrinsic features of the low-energy electronic spectrum in the BSCCO materials. These results demonstrate that the magnitude of 2Δ at 4.2 K is nearly constant in the different Tc samples, and thus, that 2Δ/kTc increases as Tc decreases. In addition, intrinsic quasiparticle excitations are detected within the gap irrespective of the sample Tc's. Analyses of these electronic spectra using a variety of pairing models suggest that gap functions having a large anisotropy can provide a good fit to the experimental data.