Unconventional vortex dynamics in the low-field superconducting phases of UPt3

The flux dynamics at low magnetic fields in $\rm UPt_3$ shows a clear distinction between the relaxation of bulk vortices and those close to the surface. In addition, in the high-temperature A-phase, vortices trapped in the bulk of the specimen after cycling it in a magnetic field creep out as expected, while bulk vortices in the B-phase remain strongly pinned, indicating that an intrinsic, novel pinning mechanism exists in the low-temperature superconducting phase of $\rm UPt_3$.