Heikki Junes

Melting curve of 4He: No sign of a supersolid transition down to 10 mK

We have measured the melting curve of 4He in the temperature range from 10 to 400 mK with the accuracy of about 0.5 micro bar. Crystals of different quality show the expected T4 dependence in the range from 80 to 400 mK without any sign of the supersolid transition, and the coefficient is in excellent agreement with available data on the sound velocity in liquid 4He and on the Debye temperature of solid 4He. Below 80 mK, we have observed a small deviation from T4 dependence, which, however, cannot be attributed to the supersolid transition, because instead of decrease the entropy of the solid rather remains constant, about 2.5 x 10(-6) R.

Experimental setup for the observation of crystallization waves in 3He

At low temperatures helium crystals can grow and melt so fast that a melting-freezing wave may propagate along the liquid-solid interface. In 4He these crystallization waves have been observed at temperatures below 0.5K. The required temperature for the observation of the crystallization waves in 3He is predicted to be about 0.2 mK. In order to reach such low temperature at the melting pressure of 3He, special care has to be taken in the design of the experimental cell. Here we present the draft of the experimental cell which is designed for observation of the crystallization waves in 3He.

On the growth dynamics of 4He crystals near the first roughening transition

The first roughening transition of a surface of hcp 4He crystals was carefully studied in Paris in 1980s. By investigating the growth dynamics of the (0001) facet, the free energy of an elementary step was measured in the close vicinity of the transition and a good agreement was found with the theory of critical fluctuations developed by Nozieres and Gallet. We believe, however, that the interpretation of the growth data near the roughening transition made by the Paris group is not self‐consistent. We argue that with the step energies they obtained, assuming that the growth is due to the process of 2D‐nucleation of terraces, another growth mechanism provided by screw dislocations should be much more effective.

Faceting of 3He crystals

Abstract We report on our optical observations on BCC 3 He crystals in the temperature range of 8– 55 mK . With our interferometric technique we were able to identify at least three different types of facets, (1 1 0), (1 0 0) , and (2 1 1) , at temperatures up to 55 mK . Previously, only the (1 1 0) facet was observed at such high temperatures.