Vortex-glass behavior in superconducting K3C60 and Rb3C60.

Abstract

The temperature and field dependence of the magnetic susceptibility of well-characterized ${\mathrm{K}}_{3}$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_{3}$${\mathrm{C}}_{60}$ show that the zero-field-cooled (ZFC) diamagnetism below ${\mathit{T}}_{\mathit{c}}$ 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 ${\mathit{T}}_{\mathit{c}}$, similar to that observed in high-${\mathit{T}}_{\mathit{c}}$ cuprates as well as disordered conventional type-II superconductors. The field dependence of the vortex glass to vortex fluid transition temperature ${\mathit{T}}^{\mathrm{*}}$ is found to follow the de Almeida--Thouless relation H=${\mathit{H}}_{0}$[1-${\mathit{T}}^{\mathrm{*}}$(H)/${\mathit{T}}^{\mathrm{*}}$(0)${]}^{\ensuremath{\gamma}}$, where \ensuremath{\gamma}=3/2 for both compounds.