Observation of anomalously fast diffusion in $^3$He-$^4$He solid solutions near the BCC-HCP transition

The pulsed NMR technique was used to investigate diffusion on the BCC-HCP phase-equilibrium and melting curves of a dilute solution of $^3$He in $^4$He. The contributions from all coexisting phases were identified using the spin-echo method. It is established that, along with the contributions from the equilibrium BCC and HCP phases or from bulk liquid (in the melting curve measurements), there is an additional diffusional process that is characterized by an anomalously high diffusion coefficient. It is found that the latter is close to the diffusion coefficient in liquid helium, while the diffusion itself is spatially restricted. The observed effect may be caused by the formation of liquid droplets in the course of the BCC-HCP transition.