Helium-3 undergoes phase transition to superfluid phase at temperatures of the order of 1 mK via spin-triplet pairing. The triplet pairing allows for multiple superfluid phases, three of which can be realized in bulk geometry. The first part of the talk concentrates on dynamics of quantized vortices in the fully-gapped topological phase, known as the B phase. In particular, I will cover experiments on the response of an equilibrium vortex lattice to perturbations such as a rapid stopping of the rotational drive (spin-down) or application of an AC component on top of the DC drive. Remarkably, the spin-down measurements show finite dissipation in the zero-temperature limit, interpreted as overheating of the vortex-core-bound fermion states by helical excitations of the vortex core. Moreover, the AC measurements reveal an energy-cascade originating from wave turbulence of quantized vortices.
The second part concentrates on vortices seen in novel superfluid phases encountered in restricted geometry. In the experiments the sample volume contains a nanostructured material consisting on nearly parallel strands smaller in diameter than the coherence length. Under these conditions, the highest-temperature superfluid phase is the polar-phase containing a Dirac nodal line in the quasiparticle energy spectrum. The polar phase supports a different variety of vortices than the bulk phases. Particular attention is paid to half-quantum vortices (HQVs) - vortices containing half a quantum of circulation plus winding of the spin space. Strong pinning of HQV cores to the confining strands allows taking the HQVs through phase transitions to other superfluid phases encountered only within nanoconfined samples - where the existence of HQVs has connections to other fields of physics such as topological quantum computing and cosmology.
Host: Nir Navon