Atomic-scale spatial modulation of zero-bias conductance in CeCoIn$_{5}$

Understanding the pairing mechanism of unconventional superconductivity has been a long-standing problem in condensed matter physics. Scanning tunneling microscopy (STM) has been utilized to pursue the pairing mechanism especially on high-$T_{C}$ cuprates and recently on the heavy fermion superconductor CeCoIn$_{5}$. However, the observed superconducting gap spectrum on CeCoIn$_{5}$ contains unexpectedly large zero-bias conductance (ZBC) even well below the critical temperature. By performing precise low-temperature STM measurements, we found that the amount of ZBC is larger on In sites and smaller on Ce sites in CeIn planes. We interpret this atomic-scale modulation as a consequence of different hybridization strengths of Ce 5$d$ and In 4$p$ bands with Ce 4$f$ band, indicating that both the unexpected ZBC and the spatial modulation are attributed to the fact that Ce 4$f$ electrons indeed play a main role for the superconductivity.