Point-contact spectroscopy of the pure and Cd-doped heavy-fermion superconductor CeCoIn$_{5}$

Point-contact spectroscopy has been performed on pure and Cd-doped CeCoIn$_{5}$. Conductance spectra of CeCoIn$_{5}$ along three different orientations exhibit consistent features: i) background asymmetry; ii) Andreev reflection signal over similar energy scales ($\sim $1 meV) and of similarly reduced magnitudes (10 - 13{\%}) at zero-bias.$^{1,2}$ Comparison with the extended Blonder-Tinkham-Klapwijk model calculations indicate the first spectroscopic evidence for $d_{x2-y2}$ symmetry of the superconducting order parameter.$^{1,2}$ A two-fluid model$^{3}$ will be discussed to explain the asymmetry and the reduced Andreev reflection. Cd-doped (10{\%}) CeCoIn$_{5}$ exhibits intriguing conductance behaviors as a function of temperature and magnetic field, undergoing antiferromagnetic and superconducting transitions: a broad zero-bias peak below $T_{N}$ and two competing conductance channels below $T_{c}$. 1.$^{ }$W.K. Park \textit{et al}., PRB \textbf{72}, 052509 (2005); cond-mat/0507353; cond-mat/0606535. 2.$^{ }$W.K. Park and L.H. Greene, PRL \textbf{96}, 259702 (2006). 3. S. Nakatsuji, D. Pines and Z. Fisk, PRL \textbf{92}, 016401 (2004). Work supported by the U.S. DoE DEFG02-91ER45439 through the FSMRL and the CMM at UIUC, by NSF-DMR-0503360 at UCD {\&} UCI, and performed at LANL under auspices of the U.S. DoE, office of Science.