Unconventional Superconductivity arising from Multipolar Kondo Interactions

Abstract

The nature of unconventional superconductivity is intimately linked to the microscopic nature of the pairing interactions. In this work, motivated by cubic heavy fermion compounds with embedded multipolar moments, we theoretically investigate superconducting instabilities instigated by multipolar Kondo interactions. Employing multipolar fluctuations (mediated by RKKY interaction) coupled to conduction electrons via two-channel Kondo and novel multipolar Kondo interactions, we uncover a variety of superconducting states characterized by higher-angular momentum Cooper pairs, J=0,1,2,3. We demonstrate that both odd and even parity pairing functions are possible, regardless of the total angular momentum of the Cooper pairs, which can be traced back to the atypical nature of the multipolar Kondo interaction that intertwines conduction electron spin and orbital degrees of freedom. We determine that different (point-group) irrep classified pairing functions may coexist with each other, with some of them characterized by gapped and point node structures in their corresponding quasiparticle spectra. This work lays the foundation for discovery and classification of superconducting states in rare-earth metallic compounds with multipolar local moments.

Investigating the An+1BnX3n+1 Homologous Series: A New Platform for Studying Magnetic Praseodymium Based Intermetallics

“… 54 Electric quadrupolar ordering has led to identification of new quantum critical points, 55 non-Fermi liquid behavior, 56 and unconventional superconductivity. 57 PrInAg 2 58 , 59 was the first heavy electron Pr compound discovered with the second largest Sommerfeld coefficient identified (γ ∼ 6.5 J/mol K 2 ). Later, a large family of heavy superconducting compounds, PrM 2 X 20 (M = Ti and V with X = Al; 56 M = Ir and Rh with X = Zn; 60 , 61 M = Ni with X = Cd 62 ), was identified where the different M and X could be varied to tune the superconducting transition temperatures, quadrupolar order, and magnetic order.…”

“…The CEF stabilized non-Kramer’s doublet ground state results in a two-channel Kondo effect through electric quadrupolar ordering . Electric quadrupolar ordering has led to identification of new quantum critical points, non-Fermi liquid behavior, and unconventional superconductivity . PrInAg 2 , was the first heavy electron Pr compound discovered with the second largest Sommerfeld coefficient identified (γ ∼ 6.5 J/mol K 2 ).…”