Thermodynamic Stability of Superfluid Flow Through a Channel

The limit of metastable existence of parallel superflow through channels is found by examining the second variation of the free energy. The corresponding critical velocity Vc1 is calculated with the quasiparticle model and with the Ginzburg-Pitaevskii theory. Vc1 reduces to the Landau velocity for T→0 and tends to zero for T→T_λ. The behavior of the system above Vc1 is discussed. There is qualitative agreement with experiments on hot ions drifting through He II.