Fine details of the nodal electronic excitations in Bi₂Sr₂CaCu₂O_8+δ

Very high energy resolution photoemission experiments on high quality samples of optimally doped Bi₂Sr₂CaCu₂O_8+δ show new features in the low-energy electronic excitations. A marked change in the binding energy and temperature dependence of the near-nodal scattering rates is observed near the superconducting transition temperature, T_C. The temperature slope of the scattering rate measured at low energy shows a discontinuity at T_C. In the superconducting state, coherent excitations are found with the scattering rates showing a cubic dependence on frequency and temperature. The superconducting gap has a d-wave magnitude with negligible contribution from higher harmonics. Further, the bilayer splitting has been found to be finite at the nodal point.