Falling 4 He crystals in superfluid

What is it about?

We report on the crystal shapes of 4He falling in superfluid subjected to a uniform superflow from beneath. Due to the coupling between the superflow and crystallization, falling 4He crystals showed a rich variety of shapes responding almost instantaneously to the surrounding superflow and boundary conditions.

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Why is it important?

While first order phase transition of classical matter under a mass or heat flow remains to be very difficult to understand and is actively discussed in statistical physics to look for general descriptions of non-equilibrium systems, this system will provide a new possibility that effect of the mass flow on the first order phase transition can be visualized by the change in crystal shape. Our finding will also shed light on the hydrodynamic instability of quantum fluids which have recently been actively investigated in the field of Bose condensed systems.