Spontaneous disordering of the Vortex Lattice in the chiral phase of UPt₃ with H parallel to c.

The unconventional, topological superconductor UPt₃ is suspected to have one chiral superconducting phase. We have performed small angle neutron scattering (SANS) from the vortex lattice (VL) in UPt₃ at the Paul Scherrer Institute, ILL, and Oak Ridge National Lab with the magnetic field parallel to the hexagonal c-axis. The VL Bragg peaks in the chiral phase show a time-dependent behavior exhibiting a clear decrease of intensity with time. This spontaneous disordering occurs when the applied magnetic field is left constant, but order can be restored by small oscillations of the applied field. The spontaneous disordering occurs faster in higher quality samples which rules out defect pinning as a cause. The process also occurs faster at higher vortex densities suggesting that vortex-vortex interactions are driving the disorder.