Superfluid Vorticity and 1/f Noise in Melting of Solid ⁴He

One of the ways to reach a zero-vorticity state in superfluid ⁴He is to melt solid helium slowly at temperatures well below Tλ. This method takes advantage of the small density difference between the liquid and solid phases and of the high critical velocities for vortex formation at low T. However, pinning of the liquid-solid interface on the walls, revealed by 1/f-like pressure fluctuations of up to 1-10 μbar in our setup, has consistently led to remanent vortex line densities of ∼ 4 · 10³ lines per cm².