Evidence for self-organized formation of logarithmic spirals during explosive crystallization of amorphous Ge:Mn layers

Logarithmic spirals are found on different length scales in nature, e.g. in nautilus shells, cyclones, and galaxies. The underlying formation laws can be related with different growth mechanisms, pressure gradients, and density waves. Here we report on the self-organized formation of symmetric logarithmic crystallization spirals in a solid material on the micrometer length scale, namely in an amorphous Ge:Mn layer on a Ge substrate. After exposure to a single light pulse of a flash lamp array, the Ge:Mn layer is crystallized and reveals a partially rippled surface and logarithmic microspirals. Finally, we present a model describing the formation of the crystallization spirals by directional explosive crystallization of the amorphous Ge:Mn layer which is triggered by the flash lamp light pulse.