Tunneling spectrum into a d-wave superconductor with a time-reversal-symmetry-broken surface state

Within a Blonder-Tinkham-Klapwijk scattering formalism, the effects of a broken-time-reversal-symmetry (BTRS) surface pairing state on the transport properties of a normal-metal-d-wave-superconductor junction have been studied by solving the Bogoliubov-de Gennes equations. It has been shown that the zero-bias conductance peak (ZBCP) exhibited in the pure d-wave case is splitted due to the shift of the midgap state energy in the presence of the BTRS state. The splitting of the ZBCP is mainly determined by the strength of the subdominant s-wave componenet breaking the time-reversal symmetry. If the surface region extends several superconducting coherence lengths, the subgap resonances in conductance take place. Very interestingly, the shift of the subgap resonance peaks is determined by the relative strength of two components of the BTRS surface order parameter, regardless of the absolute strength of them.