Quasiparticle interference in the heavy-fermion superconductor CeCoIn5

We investigate the quasiparticle interference in the heavy fermion superconductor CeCoIn5 as a direct method to confirm the d-wave gap symmetry. The ambiguity between d(xy) and d(x2-y2) symmetry remaining from earlier specific heat and thermal transport investigations has been resolved in favor of the latter by the observation of a spin resonance that can occur only in d(x2-y2) symmetry. However, these methods are all indirect and depend considerably on theoretical interpretation. Here we propose that quasiparticle interference (QPI) spectroscopy by scanning tunneling microscopy (STM) can give a direct fingerprint of the superconducting gap in real space that may lead to a definite conclusion on its symmetry for CeCoIn5 and related 115 compounds. The QPI pattern for both magnetic and nonmagnetic impurities is calculated for the possible d-wave symmetries and characteristic differences are found that may be identified by use of the STM method.