Figure 4: Transition from linear to zigzag structure.
From: Control of the conformations of ion Coulomb crystals in a Penning trap
Plot of the measured values of 
at the onset of a zigzag structure for different lengths of chain. The solid lines follow theoretical predictions calculated for different values of the rotation frequency of the crystal. The best fit suggests that these crystals were rotating at ~0.34 × Ω/2 in the laboratory frame or 0.66 × Ω/2 in the rotating frame.
