⁷⁷Se NMR studies on magic angle effect and nature of the superconducting state in the organic superconductors (TMTSF) ₂X

The ⁷⁷Se NMR spin lattice relaxation rate in (TMTSF) ₂PF ₆ in the regime of the Magic Angle Effect (MAE) exhibits no significant changes as the magnetic field orientation is rotated through the MAs, from which we conclude that there is no evidence for either a single-particle gap, or a gap in the spin excitation spectrum. Furthermore, no effect on the FISDW transition temperature was observed at the Magic Angles. As previously reported for (TMTSF) ₂PF ₆ at high pressures, the Knight shift in the superconducting state of (TMTSF) ₂ClO ₄ is inconsistent with a uniform singlet spin pairing.