Hexagonal eutectic solidification patterns operating near a marginal   stability point
  We study the long-time dynamics of hexagonal directional-solidification patterns in bulk samples of a transparent eutectic alloy using an optical method which permits real-time observation of the growth front. A slow dilatation of the patterns due to a slight curvature of the isotherms drives the system into a permanent regime, close to the threshold for the rod splitting instability. Thus an apparently minor instrumental imperfection suffices to maintain the system near a marginal stability point. This answers the long-standing question of spacing selection in bulk eutectic growth. 
Mikael Perrut (INSP, LLB), Silv\`ere Akamatsu (INSP), Sabine   Bottin-Rousseau (INSP), Gabriel Faivre (INSP)