Point-contact spectroscopy in heavy-fermion superconductors

Abstract

We develop a microscopic model to calculate point-contact spectra between a metallic tip and a superconducting heavy-fermion system. We apply our tunneling model to the heavy fermion ${\text{CeCoIn}}_{5}$, both in the normal and superconducting states. In point contact and scanning tunneling spectroscopy many heavy-fermion materials, such as ${\text{CeCoIn}}_{5}$, exhibit an asymmetric differential conductance, $dI/dV$, combined with a strongly suppressed Andreev reflection signal in the superconducting state. We argue that both features may be explained in terms of a multichannel tunneling model in the presence of localized states near the interface. We find that it is not sufficient to tunnel into two itinerant bands of light and heavy electrons to explain the Fano line shape of the differential conductance. Localized states in the bulk or near the interface are an essential component for quantum interference to occur when an electron tunnels from the metallic tip of the point contact into the heavy-fermion system.