The Two-Fluid Theory for Superfluid Hydrodynamics and Rotational Motion

The two-fluid theory for superfluid hydrodynamics is derived from the fountain pressure result that condensed bosons move at constant entropy and are driven by the chemical potential gradient. Explicit results for ${}^4$He show that the superfluid has vorticity, which is consistent with measured data but inconsistent with Landau’s principle that superfluid flow is irrotational. The macroscopic wavefunction is criticised.