Agenda

Résumé : After a brief overview of the breadth of ultra-low temperature experiments at the London Low Temperature Laboratory and underlying experimental techniques, I will present the study of interplay between superconductivity and antiferromagnetism in the heavy fermion metal YbRh₂Si₂. We observe two antiferromagnetic phases: the electronic AFM below 70 mK and electro-nuclear spin density wave (SDW) below 1.5 mK [J Knapp et al., 130, 126802 (2023)]. High-resolution measurements of the complex electrical impedance Z(T,H) as a function of temperature and magnetic field reveal multiple superconducting phases below 11 mK, both Pauli-limited and beyond the Pauli limit. We interpret the strong sample-to-sample variation and rich Z(T,H) maps in terms of heterogeneous superconductivity. The superconductivity is abruptly switched off at the critical magnetic field of the electronic AFM. The onset of electro-nuclear SDW enhances the superconductivity, which can be accounted for by the simultaneous formation of a spin-triplet pair density wave. Together these observations provide compelling evidence for spin-triplet superconductivity, and its underpinning by antiferromagnetism.