Tunneling spectra for ($d_{x^2-y^2}+is$)-wave superconductors versus tunneling spectra for ($d_{x^2-y^2}+id_{xy}$)-wave superconductors

Abstract

The tunneling conductance spectra 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 $d_{x^2-y^2}+is$, or $d_{x^2-y^2}+id_{xy}$. It is found that in the ($d_{x^2-y^2}+is$)-wave case there is a well defined conductance peak in the conductance spectra, in the amplitude of the secondary s-wave component. In the ($d_{x^2-y^2}+id_{xy}$)-wave case the tunneling 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 ($d_{x^2-y^2}+id_{xy}$)-wave state.