Quantized Vortices Beside the Superfluid-Normal Interface

We consider a quantized vortex line parallel to the interface between the concentrated (c) and dilute (d) phases of a liquid ³ He- ⁴ He mixture. The vortex produces a groove-like distortion of the interface deflected into the d-phase. As a vortex approaches the interface, the bending flexure increases, reaching a maximum of 0.65m at a critical distance of 1.3m. Closer positions become absolutely unstable. Distortion of the interface leads to strong reduction of the threshold (6.3cm/s) for the Helmholtz-Kelvin tangential instability.