Vortex-glass behavior in superconducting K3C60 and Rb3C60.

The temperature and field dependence of the magnetic susceptibility of well-characterized K[sub 3]C[sub 60] and Rb[sub 3]C[sub 60] show that the zero-field-cooled (ZFC) diamagnetism below [ital T][sub [ital c]] is irreversible for both systems, while the field-cooled (FC) curve is reversible, and that the ZFC diamagnetism is more than four times larger than the FC. This behavior is attributed to a vortex-glass state below [ital T][sub [ital c]], similar to that observed in high-[ital T][sub [ital c]] cuprates as well as disordered conventional type-II superconductors. The field dependence of the vortex glass to vortex fluid transition temperature [ital T][sup *] is found to follow the de Almeida--Thouless relation [ital H]=[ital H][sub 0][1[minus][ital T][sup *]([ital H])/[ital T][sup *](0)][sup [gamma]], where [gamma]=3/2 for both compounds.