Modeling of Tunneling Spectroscopy in High - T c Superconductors , Incorporating Band Structure , Gap Symmetry , Group Velocity , and Tunneling Directionality

A theoretical model for tunneling spectroscopy employing tight-binding band structure, dx2−y2 gap symmetry, group velocity, and tunneling directionality is studied. This is done to investigate if the model can exhibit the same wide range of characteristics observed in tunneling experiments on high-Tc superconductors. A band structure specific to optimallydoped Bi2Sr2CaCu2O8 (BSCCO) is used to calculate the tunneling density of states for a direct comparison to experimental tunneling conductance. A robust feature of the model is an asymmetric, decreasing conductance background, which is in agreement with experiment for BSCCO. The model also produces generally good agreement with the tunneling data especially in the gap region. In particular, the experimentally observed asymmetric conductance peaks can be understood with this model as a direct consequence of the dx2−y2 gap symmetry. Dip features observed at |eV | ∼ 2∆ in the experimental data are not found for any range of parameters in this model, indicating that these features are caused by other physical mechanisms such as strong coupling effects. PACS numbers: 74.20. -z, 74.50. +r, 74.72. -h, 74.72. Hs