Unconventional Pairing in Heavy Fermion Metals

TL;DR

This paper discusses the unique effects of impurities on unconventional superconductors, highlighting universal low-temperature transport properties and their implications for identifying pairing symmetries in heavy fermion metals.

Contribution

It provides insights into impurity effects on unconventional superconductors and suggests experimental methods to determine pairing symmetry in heavy fermion materials.

Findings

Impurity effects lead to universal low-temperature transport coefficients.

Thermal conductivity measurements support specific pairing symmetries in UPt3.

Universal limits depend on order parameter symmetry and impurity scattering.

Abstract

The Fermi-liquid theory of superconductivity is applicable to a broad range of systems that are candidates for unconventional pairing. Fundamental differences between unconventional and conventional anisotropic superconductors are illustrated by the unique effects that impurities have on the low-temperature transport properties of unconventional superconductors. For special classes of unconventional superconductors the low-temperature transport coefficients are {\it universal}, i.e. independent of the impurity concentration and scattering phase shift. The existence of a universal limit depends on the symmetry of the order parameter and is achieved at low temperatures $k_B T \ll \gamma \ll \Delta_0$, where $\gamma$ is the bandwidth of the impurity induced Andreev bound states. In the case of UPt$_3$ thermal conductivity measurements favor an $E_{1g}$ or $E_{2u}$ ground state. Measurements at ultra-low temperatures should distinguish different pairing states.