Spin-triplet superconductors potentially host topological excitations that are of interest for quantum information processing. We report the discovery of spin-triplet superconductivity in UTe2, featuring a transition temperature of 1.6 kelvin and a very large and anisotropic upper critical field exceeding 40 teslas. This superconducting phase stability suggests that UTe2 is related to ferromagnetic superconductors such as UGe2, URhGe, and UCoGe. However, the lack of magnetic order and the observation of quantum critical scaling place UTe2 at the paramagnetic end of this ferromagnetic superconductor series. A large intrinsic zero-temperature reservoir of ungapped fermions indicates a highly unconventional type of superconducting pairing.

Magnetism is widely considered to be a key ingredient of unconventional superconductivity.In contrast to cuprate high-temperature superconductors, antiferromagnetism in Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors 1, 2 . Consequently, three different types of magnetic order are possible. Of theses, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed 2-4 . A realization of the proposed spin-vortex crystal (SVC) order is noticeably absent. We report a magnetic phase consistent with the hedgehog variation of SVC order in Ni-and Co-doped CaKFe 4 As 4 based on thermodynamic, transport, structural and local magnetic probes combined with symmetry analysis. The exotic SVC phase is stabilized by the reduced symmetry of the CaKFe 4 As 4 structure.Our results suggest that the possible magnetic ground states in FeSCs have very similar energies, providing an enlarged configuration space for magnetic fluctuations to promote high-temperature superconductivity.

We reported a controllable way of removing excess Fe in Fe 1+y Te 0.6 Se 0.4 by annealing in a fixed amount of O 2 . Compared with the weak superconductivity induced by dilute acids, O 2 annealing can successfully induce bulk superconductivity. Proper O 2 annealing changes the temperature dependence of resistivity at low temperatures from semiconducting to metallic, which comes from the deintercalation of excess Fe. Critical current densities with field along the c-axis and ab-plane are found almost isotropic with large values of // Hc c