Waves in two-dimensional superparamagnetic dusty plasma liquids

Structure of a two-dimensional superparamagnetic system in a quadratic trap

Ground-state structures of a two-dimensional (2D) system composed of superparamagnetic charged particles are investigated by means of molecular dynamics simulation. The charged particles trapped in a quadratic potential interact with each other via the repulsive, attractive, and magnetic dipole-dipole forces. Simulations are performed within two regimes: a one-component system and a two-component system where the charged particles have the identical charge-to-mass ratio. The effects of magnetic dipole-dipole interaction, mixing ratio of the two species and confinement frequency on the ground-state structures are discussed. It is found that as the strength of the magnetic dipole increases, the charged particles tend to self-organize into chainlike structures. The two species particles exhibit different structural features, depending on the competition of electrostatic repulsive interaction, magnetic dipole-dipole interaction and confinement force. The potential lanes are observed through analyzing the global potential of the magnetic particles, which guide the unmagnetic particles aligning themselves in the direction of the potential lanes.

Anticrossing of Longitudinal and Transverse Modes in Simple Fluids

If interacting modes of the same symmetry cross, they repel from each other and become hybridized. This phenomenon is called anticrossing and is well-known for mechanical oscillations, electromagnetic circuits, waveguides, metamaterials, polaritons, and phonons in crystals, but it still remains poorly understood in simple fluids. Here, we show that structural disorder and anharmonicity, governing properties of fluids, lead to the anticrossing of longitudinal and transverse modes, which is accompanied by their hybridization and strong redistribution of excitation spectra. We combined theory and simulations for noble gases to prove the reliability of mode anticrossing in simple fluids, studied here for the first time. Our results open novel prospects in understanding collective dynamics, thermodynamics, and transport phenomena in various fluids, spanning from noble gas fluids and metallic melts to strongly coupled plasmas and molecular and complex fluids.

Waves in a quasi-two-dimensional superparamagnetic dusty plasma liquid in a trap

In a two-dimensional (2D) dusty plasma composed of superparamagnetic, charged dust grains and immersed in an external magnetic field B, the grains interact via both Yukawa and magnetic dipole-dipole potentials. Because the grains' magnetic dipole moments are induced by B, the dipole moments all lie along B. When B is tilted with respect to the normal to the dust layer, the interaction between the grains becomes anisotropic. In our previous paper [Hartmann et al., Phys. Rev. E 89, 043102 (2014)PLEEE81539-375510.1103/PhysRevE.89.043102], we studied the character of waves in such a system, confined strictly to two dimensions, without any spatial extension in the direction perpendicular to the layer. We analyzed how the dispersion of waves depends on the direction of propagation and the relative strengths of the magnetic dipole and Yukawa potentials. In this paper, we consider a more realistic quasi-2D system where the grains are confined by an external potential and can undergo small oscillations perpendicular to the layer. We analyze the effect of the strength of the confining potential on the in-plane correlations and on the wave propagation. In addition to the in-plane compressional and transverse waves, there now appears an out-of-plane transverse wave generated by the oscillation of the grains in the confining potential. The theoretical approach uses the quasi-localized charge approximation paralleled by molecular dynamics simulations.

Wakes in complex plasmas: A self-consistent kinetic theory

In ground-based experiments with complex (dusty) plasmas, charged microparticles are levitated against gravity by an electric field, which also drives ion flow in the parent gas. Existing analytical approaches to describe the electrostatic interaction between microparticles in such conditions generally ignore the field and ion-neutral collisions, assuming free ion flow with a certain approximation for the ion velocity distribution function (usually a shifted Maxwellian). We provide a comprehensive analysis of our previously proposed self-consistent kinetic theory including the field, ion-neutral collisions, and the corresponding ion velocity distribution. We focus on various limiting cases and demonstrate how the interplay of these factors results in different forms of the shielding potential.