Superconducting transitions in Hg/sub 3-//sub δ/SbF6

Hg/sub 3-//sub δ/SbF6 exhibits two distinct superconducting transitions in magnetization measurements: one at 3.7 K and one at 0.42 K with the field parallel to the c axis. The high-temperature transition at 3.7 K has a partial Meissner effect and a critical field near 400 G. The low-temperature transition at 0.42 K has a complete Meissner effect and a critical field of 15.4 G. In between these two transitions is a region where flux exclusion increases approximately linearly with decreasing temperature at a rate of 0.17 G/K for an applied field of 10.9 G. The flux exclusion is approximately 7% of complete flux exclusion at the onset of the low-temperature transition. The high-temperature transition is due to bulklike mercury regions containing less than 2% of the entire mercury in the sample. Superconductivity at the low-temperature transition is intrinsic to the compound