VORTEX-GLASS BEHAVIOR IN SUPERCONDUCTING K3C60 AND RB3C60

The temperature and field dependence of the magnetic susceptibility of well-characterized K3C60 and Rb3C60 show that the zero-field-cooled ( ZFC) diamagnetism below T(c) is irreversible for both systems, while t he field-cooled (FC) curve is reversible, and that the ZFC diamagnetis m is more than four times larger than the FC. This behavior is attribu ted to a vortex-glass state below T(c), similar to that observed in hi gh-T(c) cuprates as well as disordered conventional type-II supercondu ctors. The field dependence of the vortex glass to vortex fluid transi tion temperature T is found to follow the de Almeida-Thouless relatio n H=H-0[1-T(H)/T*(0)]gamma, where gamma = 3/2 for both compounds.