Dynamics of spinning particle pairs in a single-layer complex plasma crystal

Abstract

Spontaneous formation of spinning pairs of particles, or torsions was studied in a single-layer complex plasma crystal by reducing the discharge power at constant neutral gas pressure. At higher gas pressures, torsions spontaneously formed below a certain power threshold. Further reduction of the discharge power led to the formation of multiple torsions. However, at lower gas pressures the torsion formation was preceded by the mode-coupling instability (MCI). The crystal dynamics were studied with the help of the fluctuation spectra of crystal particles’ in-plane velocities. Surprisingly, the spectra of the crystal with torsions and MCI are rather similar and contain “hot spots” at similar locations on the (k, ω) plane, despite very different appearances of the respective particle trajectories. The torsion rotation speed was close (slightly below) to the maximum frequency of the in-plane compressional mode. When multiple torsions formed, their rotation speeds were distributed in a narrow range slightly below the maximum frequency.