Zero-bias peak in tunneling spectra of high-Tc superconductors and its splitting

Effects of impurities on the conductance in normal-metal/d-wave superconductor junctions are discussed. By using the single-site approximation, it is shown that the impurity scattering causes the split of the zero-bias conductance peak (ZBCP). So far, the split of the ZBCP at the zero magnetic field has been believed to be a strong evidence of the broken time reversal symmetry states at a surface of a high-Tc superconductor. However we conclude that the impurity scattering is also responsible for the split of the ZBCP