Momentum dependence of the energy gap in the superconducting state of   optimally doped Bi2(Sr,R)2CuOy (R=La and Eu)
  The energy gap of optimally doped Bi2(Sr,R)2CuOy (R=La and Eu) was probed by angle resolved photoemission spectroscopy (ARPES) using a vacuum ultraviolet laser (photon energy 6.994 eV) or He I resonance line (21.218 eV) as photon source. The results show that the gap around the node at sufficiently low temperatures can be well described by a monotonic d-wave gap function for both samples and the gap of the R=La sample is larger reflecting the higher Tc. However, an abrupt deviation from the d-wave gap function and an opposite R dependence for the gap size were observed around the antinode, which represent a clear disentanglement between the antinodal pseudogap and the nodal superconducting gap. 
Y Okada, T Takeuchi, M Ohkawa, A Shimoyamada, K Ishizaka, T Kiss, S   Shin, H Ikuta