Surface of a He-3 crystal: Crossover from quantum to classical behavior.

He-3 crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature. To understand the reason for that, we have performed the first quantitative investigation on the growth dynamics of the basic (110) facet at 60-110 mK. The obtained values of the step free energy suggest an extremely weak coupling of the solid-liquid interface to the crystal lattice which we show to be the result of quantum fluctuations of the interface. The renormalization group approach by Nozieres and Gallet, modified to incorporate quantum fluctuations, explains well the temperature dependence of the step energy measured in this work and at ultralow temperatures by Tsepelin et al., where the coupling is known to be strong. We have thus shown that, paradoxically, the role of quantum fluctuations is at higher temperatures much larger than at low temperature

Faceting of He-3 crystals.

We report on our optical observations on BCC He-3 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

Growth dynamics and faceting of He-3 crystals.

He-3 crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature. To find out the reason for this discrepancy, we have performed the first quantitative investigation on the growth dynamics of the faceted and rough surfaces of He-3 crystals in the temperature range of 60-110 mK. We have applied an original method to obtain the variation of the overpressure on the crystal surface by measuring its curvature and height locally using a Fabry-Perot interferometer. The growth of the rough surface was found to be limited by the transport of the latent heat which elaborates in the liquid, in accordance with theoretical predictions (Puech L., et al. in J. Low Temp. Phys. 62:315, 1986; Graner F., et al. in J. Low Temp. Phys. 75:69, 1989 and 80:113, 1990) and previous measurements near the minimum of the melting curve (Graner F., et al. in J. Low Temp. Phys. 75:69, 1989 and 80:113, 1990). The mobility of an elementary step on a facet was shown to be limited by the latent heat transport as well. The values obtained for the step free energy are by two orders of magnitude smaller than at ultra low temperatures, which we show to be the result of quantum oscillations of the solid-liquid interface, which quickly become damped when temperature decreases below 100 mK

Measurements on the surface tension of He-3 crystals near 100 mK.

He-3 crystals start to show facets on their surface only at about 100 mK, well below the roughening transition temperature, and the reason for this change of the surface state is not clear yet. However, the most important characteristic of the crystal surface, the surface tension, was not measured in this temperature range before. We report our observations on the equilibrium shape of the He-3 crystals in the temperature range of 77...110 mK. The surface tension was found to be isotropic and temperature-independent, and the corresponding value of the capillary length, lambda = 0.93 +/- 0.10 mm, is in a good agreement with the value measured at higher temperatures by Rolley et al