Point-contact spectroscopy in heavy-fermion superconductors

TL;DR

This paper presents a minimal tunneling model to explain the asymmetric conductance and suppressed Andreev reflection observed in point-contact spectroscopy of heavy-fermion superconductor CeCoIn5, emphasizing the role of localized states.

Contribution

It introduces a multichannel tunneling model incorporating localized states to accurately describe spectroscopic features in heavy-fermion superconductors.

Findings

Localized states are crucial for quantum interference effects.

Two-band tunneling models are insufficient to explain Fano line shapes.

The model successfully reproduces experimental conductance asymmetries.

Abstract

We develop a minimal 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 CeCoIn5, both in the normal and superconducting state. In point-contact and scanning tunneling spectroscopy many heavy-fermion materials, like CeCoIn5, 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.