We compare the local magnetization at a spatial singularity of superconducting ${\mathrm{U}}_{0.97}$${\mathrm{Th}}_{0.03}$${\mathrm{Be}}_{13}$ for different magnetic field histories. We find a reduction in the zero-field-cooled vortex flow relative to the field-cooled case, marked by a sharp onset coincident in temperature with the second (lower-temperature) transition in the specific heat. This effect is peculiar to the flux threading the hole of the torus, to (U,Th)${\mathrm{Be}}_{13}$ samples with multiple superconducting transitions, and to the lower superconducting state with broken time-reversal invariance.

• Received 13 February 1995

DOI:https://doi.org/10.1103/PhysRevB.51.12041