Coexistence of ferromagnetic fluctuations and superconductivity in the actinide compound UTe2

Synopsis

Superconductivity with spin-triplet pairing symmetry is quite rare in nature and only a handful of materials have been recognized so far in this category. Very recently (Science 2019), superconductivity has been discovered in a new actinide compound UTe2, Tc ~ 1.6 K. Superconductivity in this material seems to involve spin-triplet pairing due to a very large and highly anisotropic upper critical field and a temperature independent NMR Knight shift across Tc.  Bulk magnetization measurements show the presence of magnetic fluctuations which are associated with the metallic ferromagnetic quantum critical point. Mu-SR studies performed in zero field configuration below 5K show the continuous slowing down of magnetic fluctuation even across Tc and record no signature of long-range or local magnetic ordering down to 20 mK. The dynamic relaxation rate as a function of temperature agrees well with the self-consistent renormalization theory of spin fluctuations for a three-dimensional weak itinerant ferromagnetic metal. The magnetic volume sensed above and below Tc using weak transverse-field mu-SR measurements suggests that the superconducting state is coexisting with magnetic fluctuations in the compound. In addition, recent developments to the understanding of superconductivity in this material will also be discussed.