Investigations of magnetism in pure and Th-doped UTe₂ by μSR

The application of the muon spin relaxation/rotation (μSR) technique to condensed matter systems utilizes implanted positively charged spin-polarized muons as a local probe of static and dynamic magnetism. With our collaborators we have used μSR to investigate magnetism in the bulk of UTe₂ single crystals. At issue is the nature of the magnetic interactions and their role in the pairing mechanism that gives rise to what appears to be a rare topological spin-triplet superconducting state. I will first summarize our experimental results on pure UTe₂ that provide evidence for the occurrence of ubiquitous magnetic clusters, which gradually freeze upon cooling through the superconducting transition temperature (T_c) to form an inhomogeneous frozen state at low temperatures [1,2]. I will then present our recent μSR experimental results on Th-doped UTe₂ and measurements of pure UTe₂ in high magnetic field. Potential implications of our findings for understanding and establishing the intrinsic physical properties of UTe₂ will be discussed.