Triplet Superconductivity in an Organic Superconductor Probed by NMR Knight Shift

The nature of the superconducting state in quasi-one-dimensional organic conductors has remained controversial since its discovery. Here we present results of (77)Se NMR Knight shift (K(s)) experiments in (TMTSF)(2)PF(6) under 7 kbar of pressure with a magnetic field aligned along the most conducting a axis. We find no noticeable shift in K(s) upon cooling through the superconducting transition. Since K(s) directly probes the spin susceptibility chi(s), the fact that chi(s) remains unchanged through the superconducting transition strongly suggests spin-triplet superconductivity.