Universal heat transport in a heavy-fermion superconductor

TL;DR

This study demonstrates universal heat transport in the heavy-fermion superconductor CeIrIn5, revealing a uniaxial anisotropy that indicates a basal-plane line of nodes, challenging the previously assumed d-wave symmetry and suggesting different pairing mechanisms in related compounds.

Contribution

It provides the first evidence of directional-dependent universal heat transport in CeIrIn5, indicating a specific nodal structure and challenging existing symmetry models for similar heavy-fermion superconductors.

Findings

Heat conduction in CeIrIn5 is universal perpendicular to the crystal axis.

Anisotropic heat transport suggests a line of nodes in the basal plane.

Contrasts with d-wave symmetry proposed for CeCoIn5.

Abstract

The symmetry of the order parameter is the defining property of a superconductor and a strong clue to its pairing mechanism. While d-wave symmetry is firmly established in high-Tc superconductors, in no heavy-fermion superconductor is the symmetry known definitively. One way to elucidate the order parameter is to locate the symmetry-imposed nodes in the energy gap by measuring the heat carried by the zero-energy quasiparticles associated with those nodes as a function of direction. As verified in high-Tc superconductors a line of nodes yields universal heat transport independent of impurity scattering. Here we show that heat conduction in the heavy-fermion superconductor CeIrIn5 is also universal, but only for a current perpendicular to the tetragonal axis of its crystal structure, not parallel to it. This uniaxial anisotropy is strong evidence for a line of nodes in the basal plane, which is inconsistent with the d-wave symmetry proposed for the isostructural superconductor CeCoIn5. Different symmetries in the two materials would explain why the phase diagram of these heavy-fermion compounds consists of two separate superconducting domes.