Solid-State $$\mathrm {^3He}$$ NMR of the Superconducting Rubidium Endofulleride $$\mathrm {Rb_3(^3He@C_{60})}$$

Abstract A new variant of the superconducting fulleride Rb $$_3$$ 3 C $$_{60}$$ 60 is presented, with $$^3$$ 3 He atoms encapsulated in the C $$_{60}$$ 60 cages. The $$^3$$ 3 He nuclei act as sensitive NMR probes embedded in the material. The superconducting and normal states are characterized by $$^3$$ 3 He NMR. Evidence is found for coexisting vortex liquid and vortex solid phases below the superconducting transition temperature. A strong dependence of the spin–lattice relaxation time constant on spectral frequency is observed in the superconducting state, as revealed by two-dimensional NMR utilizing an inverse Laplace transform. Surprisingly, this phenomenon persists, in attenuated form, at temperatures well above the superconducting transition.