Modeling of tunneling spectroscopy in high-Tcsuperconductors incorporating band structure, gap symmetry, group velocity, and tunneling directionality

Abstract

A theoretical model for tunneling spectroscopy employing tight-binding band structure, $d_{x^2-y^2}$ 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-$T_c$ superconductors. A band structure specific to optimally-doped ${\mathrm{Bi}}_2{\mathrm{Sr}}_2{\mathrm{CaCu}}_2{\mathrm{O}}_8$ (Bi-2212) 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 Bi-2212. 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 $d_{x^2-y^2}$ gap symmetry. Dip features observed at |eV|∼2Δ 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.