Tunnelling spectra for (dx2-y2+is)-wave superconductors versus tunnelling spectra for (dx2-y2+idxy)-wave superconductors

The tunnelling conductance spectrum of a normal-metal/insulator/singlet superconductor is calculated from the reflection amplitudes using the Blonder-Tinkham-Klapwijk (BTK) formulation. The pairing symmetry of the superconductor is assumed to be d(x2-y2) + is or d(x2-y2) + id(xy). It is found that in the (d(x2-y2) + is)-wave case there is a well defined conductance peak in the conductance spectra, in the amplitude of the secondary s-wave component. In the (d(x2-y2) + id(xy))-wave case the tunnelling conductance has residual values within the gap, due to the formation of bound states. The bound-state energies depend on the angle of the incident quasiparticles, and also on the boundary orientation. On the basis of this observation, an electron-focusing experiment is proposed to probe the (d(x2-y2) + id(xy))-wave state.