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_3C_{60} is presented, with ^3He atoms encapsulated in the C_{60} cages. The ^3He nuclei act as sensitive NMR probes embedded in the material. The superconducting and normal states are characterized by ^3He 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.