An unusual superconductor: In conventional, and in many unconventional, superconductors, the electrons that form Cooper pairs have spins pointing in opposite directions. An applied magnetic field can easily “break” such pairs—and destroy superconductivity—by aligning both spins in the same direction. In contrast, spin-triplet superconductors are much more resilient to magnetic fields. Very few candidates for such materials have been discovered. Ran et al. add to this select group by observing signatures of spin-triplet superconductivity, including a very large and anisotropic upper critical magnetic field, in the material UTe ₂ . Because spin-triplet superconductors may naturally exhibit topological superconductivity, this material may also be of interest in quantum computing. Science , this issue p. 684

Magnetism is widely considered to be a key ingredient of unconventional superconductivity. In contrast to cuprate high-temperature superconductors, antiferromagnetism in most Fe-based superconductors (FeSCs) is characterized by a pair of magnetic propagation vectors, (π,0) and (0,π). Consequently, three different types of magnetic order are possible. Of these, only stripe-type spin-density wave (SSDW) and spin-charge-density wave (SCDW) orders have been observed. 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-doped and Co-doped CaKFe₄As₄ 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 CaKFe₄As₄ 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 report ${}^{75}\mathrm{As}$ nuclear magnetic resonance (NMR) studies on a new iron-based superconductor, ${\mathrm{CaKFe}}_4{\mathrm{As}}_4$, with $T_{\mathrm{c}}=35$ K. ${}^{75}\mathrm{As}$ NMR spectra show two distinct lines corresponding to the As(1) and As(2) sites close to the K and Ca layers, respectively, revealing that K and Ca layers are well ordered without site inversions. We found that nuclear quadrupole frequencies ${\nu }_{\mathrm{Q}}$ of the As(1) and As(2) sites show an opposite temperature $T$ dependence. Nearly $T$ independent behavior of the Knight shifts $K$ is observed in the normal state, and a sudden decrease in $K$ in the superconducting (SC) state suggests spin-singlet Cooper pairs. ${}^{75}\mathrm{As}$ spin-lattice relaxation rates $1/T_1$ show a power-law $T$ dependence with different exponents for the two As sites. The isotropic antiferromagnetic spin fluctuations characterized by the wave vector $\mathbf{q}=(\pi ,0)$ or $(0,\pi )$ in the single-iron Brillouin zone notation are revealed by $1/T_{1}T$ and $K$ measurements. Such magnetic fluctuations are necessary to explain the observed temperature dependence of the ${}^{75}\mathrm{As}$ quadrupole frequencies, as evidenced by our first-principles calculations. In the SC state, $1/T_1$ shows a rapid decrease below $T_{\mathrm{c}}$ without a Hebel-Slichter peak and decreases exponentially at low $T$, consistent with an $s^{\pm }$ nodeless two-gap superconductor.

As a p-type multifunctional semiconductor, CuSe nanostructures show great promise in optoelectronic, sensing, and photocatalytic fields. Although great progress has been achieved, controllable synthesis of CuSe nanosheets (NSs) with a desirable spacial orientation and open frameworks remains a challenge, and their use in supercapacitors (SCs) has not been explored. Herein, a highly vertically oriented and interpenetrating CuSe NS film with open channels is deposited on an Au-coated polyethylene terephthalate substrate. Such CuSe NS films exhibit high specific capacitance (209 F g^–1) and can be used as a carbon black- and binder-free electrode to construct flexible, symmetric all-solid-state SCs, using polyvinyl alcohol–LiCl gel as the solid electrolyte. A device fabricated with such CuSe NS films exhibits high volumetric specific capacitance (30.17 mF cm^–3), good cycling stability, excellent flexibility, and desirable mechanical stability. The excellent performance of such devices results from the vertically oriented and interpenetrating configuration of CuSe NS building blocks, which can increase the available surface and facilitate the diffusion of electrolyte ions. Moreover, as a prototype for application, three such solid devices in series can be used to light up a red light-emitting diode.