Persistent currents in T1-Ba-Ca-Cu-O superconductor.

We have demonstrated the presence of circulating circumferential currents in toroids at a T1-Ba-Ca-Cu-O superconductor at 77. 3K and 90.2K. The nominal composition was T1 sub (1.5) Ba sub 2 Ca sub 2 Cu sub 3 O sub x, however both the x-ray diffraction pattern and the Meissner effect indicate the presence of more than one phase. The circulating current was found to decrease by 27% in 3.8 x 10 sup 3 seconds. The nature of the above time dependence is not consistent with the presence of a simple ohmic resistance but rather indicates that a process such as flux creep is the cause of this decay. An estimated upper limit of the resistivity is 1.3 x 10 sup (-14) OMEGA cm at 77.3K.