Comment on "Experimental determination of superconducting parameters for the intermetallic perovskite superconductor MgCNi$_3$"

TL;DR

This paper critiques a previous study on MgCNi$_3$, arguing that thermal effects, not single-particle tunneling, explain the conductance data, thus questioning claims about unconventional pairing or strong-coupling superconductivity.

Contribution

It challenges prior interpretations of conductance measurements in MgCNi$_3$, emphasizing the role of thermal effects over single-particle tunneling.

Findings

Thermal effects likely dominate conductance measurements in MgCNi$_3$ junctions.

No evidence for unconventional pairing or strong-coupling superconductivity from the analyzed data.

Previous interpretations based on single-particle tunneling are probably incorrect.

Abstract

In a recent paper (Phys. Rev. {\bf B 67}, 094502 (2003)) Mao et al. investigated the bias-dependent conductance of mechanical junctions between superconducting MgCNi$_3$ and a sharp W tip. They interpreted their results in terms of 'single-particle tunneling'. We show it is more likely that current transport through those junctions is determined by thermal effects due to the huge normal-state resistivity of MgCNi$_3$. Therefore no conclusion can be drawn about the possible unconventional pairing or strong-coupling superconductivity in MgCNi$_3$.