| Popis: |
For large molar volume the solids of 4He have the unique feature that, in contrast to normal systems, the average random excursion of an atom from its equilibrium position is a significant fraction (~ 1/3) of the interatomic spacing. The weak interatomic interaction, which is known from measurements on the gas phase, and the light mass combine to produce crystals whose lattice dynamics cannot be described within the context of classical theory. For these reasons helium crystals are expected to be ideal systems with which one can test the subtle predictions of the quantum mechanical many-body theory of crystal dynamics. |
