Abstract
The authors show that topological superfluid 3He can flow without friction in a phase which possesses a line of zero energy in the excitation spectrum, although the Landau's limit for superflow is zero. The flow expands the node line to a Fermi surface for Bogoliubov quasipartices, which is usually absent in Cooper-paired systems, but may appear in unconventional superconductors and superfluids with certain broken symmetries.
Highlights
The stability of superflow in superfluids and superconductors is supported by both topology and the Landau criterion
We study the stability of superflow starting from the initial state prepared by slowly cooling the stationary sample through the superfluid transition in a transverse magnetic field to suppress the formation of both halfquantum vortices (HQV) and single-quantum phase vortices (SQV) [33]
If the magnetic field is applied transverse to the rotation axis and the NAFEN strands, HQVs become energetically unfavorable [42], and an array of SQVs is created on cooling through Tc
Summary
The stability of superflow in superfluids and superconductors is supported by both topology and the Landau criterion. The superflow above the Landau critical velocity remains stable until some other critical velocity vc is reached This can be either the velocity at which ρn(T = 0) = ρ and the superfluid density ρs = ρ − ρn vanishes, or the critical velocity at which quantized vortices or other topological defects, such as skyrmions, are created. The purpose of the current Report is twofold: First, we experimentally demonstrate that the superflow in the presence of the nodal line remains stable until the fluid velocity at the sample boundaries reaches 0.24 cm/s, well above the zero Landau critical velocity. Vortices remain in the sample for days after the rotation is stopped, maintaining long-living superflow exceeding the Landau critical velocity even in a stationary sample These observed features of vortex dynamics in the polar phase are supported by numerical simulations. For characterization of the effects of the BFS on superfluid properties in future experiments
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