Impurity Scattering and Gap Structure in the Anisotropic Superconductor UPt$_3$

TL;DR

This study investigates the gap structure of the heavy fermion superconductor UPt$_3$ through thermal conductivity measurements, revealing the presence of nodes along the c-axis and challenging previous assumptions about its quasiparticle excitations.

Contribution

The paper provides experimental evidence for anisotropic gap nodes in UPt$_3$, contradicting earlier interpretations of gapless behavior from specific heat data.

Findings

No linear term in thermal conductivity as T→0, indicating absence of zero energy quasiparticles.

Non-zero anisotropy ratio $rac{\kappa_c}{\kappa_b}$ at low temperatures, confirming c-axis nodes.

Nodes along the c-axis are not point nodes with linear k-dependence, as recent calculations suggest.

Abstract

The thermal conductivity, $\kappa$, of the heavy fermion superconductor UPt$_3$ was measured down to T$_c$/10. The absence of a linear term in the temperature dependence as T$\rightarrow$0 strongly suggests there are no zero energy quasiparticle excitations, in contradiction with the gapless behaviour often inferred from specific heat. A non-vanishing anisotropy ratio $\kappa_c$/$\kappa_b$ as T$\rightarrow$0 establishes a new property of the gap structure: the presence of nodes along the c-axis. Furthermore, recent calculations by Fledderjohann and Hirschfeld show these cannot be point nodes with a linear k-dependence.