Local tunneling characteristics near a grain boundary of ad-wave superconductor as probed by a normal-metal or a low-Tc-superconductor STM tip

Abstract

We study the local single-particle tunneling characteristics [as observed with scanning tunnel microscopy (STM)] for N-D and S-D tunneling, where D is a d-wave superconductor with a {100}|{110} grain boundary. The tunneling Hamiltonian method is used. The self-consistent order parameter is first determined using the quasiclassical Green's-function method, and then the tunneling characteristics at various distances from the interface, reflectivity of the interface, and temperature, are studied. For N-D tunneling, a zero-bias conductance peak (ZBCP) occurs near the interface, with diminishing magnitude away from it. For S-D tunneling, the ZBCP splits to exhibit the gap of the s-wave low-${T}_{c}$ superconducting tunneling tip, and there is a range of negative conductance just outside the peaks, when the tunneling point is near the grain boundary. The results are compared with those obtained by using a constant order parameter in each grain.