Study Of Shock Waves And Solitons In Bulk Superfluid He-4

Properties of shock waves and solitons in superfluid He-4 were studied by time-resolved shadowgraph experiments and theoretical density functional theory calculations. Pressure estimates for shock waves and the bright soliton limit (0.2 MPa) were provided and compared with the semiclassical Rankine-Hugoniot theory. Overall, the shock wave amplitude-velocity relationship was observed to be linear at least up to 175 kg/m(3). At high amplitudes, the shock waves decay into sound waves in the wake as well as a bright soliton train in the front. This suggests that the experimental shadowgraph data presented by Ancilotto et al. [Phys. Rev. Lett. 120, 035302 (2018)] correspond to such a train structure rather than an individual bright soliton. With reference to theoretical calculations, a new approach based on an accelerating wall embedded in the liquid is proposed for generating single solitons in superfluid helium. This process is also predicted to produce dark solitons in superfluid helium, which have not yet been observed experimentally. At low soliton amplitudes, collision with an exponentially repulsive wall results in nearly lossless reflection, which is accompanied by soliton inversion from dark to bright or bright to dark.