Spin-triplet superconductivity in K2Cr3As3

A spin-triplet superconductor can harbor Majorana bound states that can be used in topological quantum computing. Recently, K2Cr3As3 and its variants with critical temperature Tc as high as 8 kelvin have emerged as a new class of superconductors with ferromagnetic spin fluctuations. Here, we report a discovery in K2Cr3As3 single crystal that the spin susceptibility measured by As-75 Knight shift below T-c is unchanged with the magnetic field H-0 applied in the ab plane but vanishes toward zero temperature when H-0 is along the c axis, which unambiguously establishes this compound as a spin-triplet superconductor described by a vector order parameter (d) over right arrow parallel to the c axis. Combining with point nodal gap, we show that K2Cr3As3 is a new platform for the study of topological superconductivity and its possible technical application.