Liquid-solid interface of He has been investigated down to mK-temperatures using an optical interferometer in combination with a sensitive pressure gauge. The c-facets with 5-100 screw dislocations/cm2 grew with spiral growth which can be understood by including inertial terms and localization of steps to the standard theory. Crystals without screw dislocations revealed two novel growth mechanisms. At growth rates > 1 nm/s, these high-quality crystals grew in a burst-like manner, creating abruptly 200-2000 new atomic layers. At rates below 0.5 nm/s, the c-facet revealed slow, continuous growth. Studies of a-facets yielded a velocity vs. pressure dependence which can be explained by spiral growth. The shape of the c-facet was monitored down to 2 mK without any evidence of the freezing of kinks. Pressure measurements down to our minimum temperature did not show any anomalies connected with the supersolid transition. Indications of new faceting transitions were not observed down to 2 mK.
- optical interferometer
- superfluid 4He