Elementary steps on the He-4 crystal interface probed by He-3 atoms

The growth dynamics of c facets, governed by individual Frank-Read type of sources, has been studied at millikelvin temperatures in the presence of small concentrations of He-3 atoms in the liquid. We find that in the spiral growth regime, interaction of He-3 atoms with moving elementary steps on the surface results in additional friction. Our results are compared with theory, where high-frequency (omega greater than or equal to T/(h) over bar) zero-point oscillations of the steps are taken into account. There is a good agreement if we assume the amplitude of these oscillations xi approximate to 5 nm