  Nonunitary superconductivity is a rare and striking phenomenon in which spin
up and spin down electrons segregate into two different quantum condensates.
Because they support topological excitations, such superconductors are being
seriously considered for potential quantum information applications. We report
the discovery of nonunitary spin-triplet superconductivity in UTe2, featuring
the high transition temperature of 1.6 K and a remarkably large and anisotropic
upper critical field exceeding 40 T. In this unusual superconducting state,
electrons with parallel spins pair, yet only half of the available electrons
participate, yielding a spin-polarized condensate that coexists with a
spin-polarized metal. The superconducting order parameter, which breaks both
gauge and time reversal symmetries, arises from strong ferromagnetic
fluctuations, placing UTe2 as the paramagnetic end member of the ferromagnetic
superconductor series. This discovery yields a new platform for encoding
information using topological excitations and for manipulation of spinpolarized
currents.
