Solid-state ${}^3\mathrm{He}$ NMR of the superconducting rubidium endofulleride $\mathrm{R}{\mathrm{b}}_3{(}^{3}He@{\mathrm{C}}_{60})$

Abstract

A new variant of the superconducting fulleride $\mathrm{R}{\mathrm{b}}_3{\mathrm{C}}_{60}$ is presented, with ${}^3\mathrm{He}$ atoms encapsulated in the ${\mathrm{C}}_{60}$ cages. The ${}^3\mathrm{He}$ nuclei act as sensitive NMR probes embedded in the material. The superconducting and normal states are characterised by ${}^3\mathrm{He}$ NMR. Evidence is found for co-existing 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 utilising an inverse Laplace transform. Surprisingly, this phenomenon persists, in attenuated form, at temperatures well above the superconducting transition.

20 pages, 15 figures