Equilibrium crystal shape of 4He under microgravity

Abstract

The growth coefficient of 4He crystal which is grown from the superfluid becomes divergently large towards T=0, and the crystal relaxes to the equilibrium state in a very short period. We have succeeded in cooling 4He crystal down to 150 mK by the specially designed dilution refrigerator under microgravity of parabolic flight for 20 seconds. Using this fridge, we were able to obtain beautiful pictures of the crystal with 3 facets, c-, a-, and s-, under the equilibrium condition at 150 mK for the first time.