H. Alles, H. Junes, J. Simpura, and I.A. Todoshchenko.
Visitors: S. Balibar, R. Jochemsen, and A.Ya. Parshin.
Helium crystals provide a good model system for verification of different theoretical concepts concerning the study of all crystal surfaces and on top of that they have several interesting properties related to their quantum nature. During recent years the INTERFACE group has been studying the shape and growth dynamics of the body-centered cubic (bcc) 3He crystals along their melting curve from 0.5 mK up to several hundreds of mK. As the first significant result, more than ten different types of facets (smooth flat crystal faces) were identified and the velocities of these facets were measured as a function of the applied overpressure. The next set of experiments was performed near the magnetic ordering temperature of a bulk solid 3He, TN = 0.93 mK. In these studies it was found that the facets grow with two different mechanisms. Additionally to the well-known spiral growth, a slower growth mode, characterized with a very small growth anisotropy in the ordered state, was discovered. It was also observed that the mobility of the (100) type of facets is strongly suppressed above the transition. This is surprising because in the disordered paramagnetic phase the slowest facets were expected to be of the (110) type which have the largest interplanar distance in the bcc-lattice.
Careful measurements on the growth dynamics of 3He crystals were carried out also near 100 mK, the highest temperature at which the facets have been detected in 3He. From the experimental data the step free energies of the (110) facets at different temperatures were extracted. By applying the renormalized group theory developed by Nozières and Gallet to the measured temperature dependence, it was found that the coupling of the liquid-solid interface is uniquely weak in 3He.
Alles, H., Babkin, A., Jochemsen, R., Parshin, A.Ya., Todoshchenko, I.A., and Tsepelin, V., Faceting and growth kinetics of 3He crystals, Physica B, 329-333 (2003), pp 360-363.
Todoshchenko, I.A., Alles, H., Junes, H.J., Parshin, A.Ya., Tsepelin, V., Faceting of 3He crystals, Physica B, 329-333 (2003), pp 386-387.