Spins, electrons and broken symmetries: realizations of two channel Kondo physics

TL;DR

This paper reviews two exotic phases arising from two-channel Kondo physics in heavy fermion materials, focusing on hastatic order and composite pair superconductivity, and discusses their realizations and differences.

Contribution

It provides a comparative analysis of hastatic order and composite pair superconductivity, highlighting their mechanisms and potential material realizations.

Findings

Hastatic order linked to non-Kramers doublets and virtual valence fluctuations.

Composite pair superconductivity involves charge 2e channels and valence fluctuations.

Potential realizations in actinide and rare earth compounds like URu2Si2.

Abstract

Adding a second Kondo channel to heavy fermion materials reveals new exotic symmetry breaking phases associated with the development of Kondo coherence. In this paper, we review two such phases, the "hastatic order" associated with non-Kramers doublet ground states, where the two-channel nature of the Kondo coupling is guaranteed by virtual valence fluctuations to an excited Kramers doublet, and "composite pair superconductivity," where the two channels differ by charge 2e and can be thought of as virtual valence fluctuations to a pseudo-isospin doublet. The similarities and differences between these two orders will be discussed, along with possible realizations in actinide and rare earth materials like URu2Si2 and NpPd5Al2.