Comment on Recent Tunneling Measurements on Bi-2212
  The asymmetry in the conductance peaks shown in recent PCT and STM measurements may be a signature of the d-wave gap. This is based on our model for the tunneling density of states (DOS) which incorporates the group velocity, tunneling directionality, and a realistic band structure. We also make the comparison with the isotropic s-wave and extended s-wave gap symmetries. Whereas the asymmetry of the conductance peaks for the isotropic s-wave tends to reflect the normal state DOS, the asymmetry for the extended s-wave is opposite to that of the d-wave gap. The model shows that a change in the gap symmetry from d-wave to extended s-wave may be accompanied by a switching in the conductance peaks asymmetry. 
Z. Yusof, L. Coffey