Nonlinear Magnetoplasmons in Strongly Coupled Yukawa Plasmas

Abstract

The existence of plasma oscillations at multiples of the magnetoplasmon frequency in a strongly coupled two-dimensional magnetized Yukawa plasma is reported, based on extensive molecular dynamics simulations. These modes are the analogues of Bernstein modes which are renormalized by strong interparticle correlations. Their properties are theoretically explained by a dielectric function incorporating the combined effect of a magnetic field, strong correlations and finite temperature.PACS numbers: 52.27.Gr, 52.27.Lw Two-dimensional (2D) systems with strong correlations, i.e. with the interaction energy exceeding the thermal energy, show a number of unusual properties ranging from anomalous phase transitions (Kosterlitz-Thouless scenario), to anomalous transport, e.g. [1,2]. Examples include electrons on helium droplets and in quantum dots [3], ions in traps [4] and dusty plasmas, e.g. [5,6]. A particular correlation effect is observed in the collective oscillation spectrum of 2D Coulomb and Yukawa liquids [5,7,8] where a transverse shear mode has been predicted by Kalman and Golden [9,10]. This mode does not exist in an ideal system but has experimentally been observed in strongly coupled systems [11,12]. Similarly, in the presence of a strong magnetic field a 2D plasma shows two coupled modes -a magnetoplasmon and a magentoshear mode (upper and lower hybrid modes) which have recently been studied in detail in the liquid and crystal phases [6][7][8].Here we show that a strongly correlated 2D Yukawa plasma (2DYP) possesses additional collective modes. We demonstrate that these are related to Bernstein modes (BM) [13] which are well known in hightemperature classical, e.g. [14,15] and quantum plasmas, e.g. [16,17]. However, these are all nearly ideal plasmas. Here we demonstrate that such modes can also exist in strongly correlated systems but they have a number of peculiar properties arising from the combined effect of correlations and the magnetic field.Model and simulation method. Our 2DYP consists of N particles in a quadratic monolayer (with periodic boundary conditions), subject to a magnetic field perpendicular to the plane and interacting by Yukawa forces. The coupled Newton's equations are (i = 1 . . . N )with the Debye screening length λ D and charge Q.Here we define the Wigner-Seitz radius a = (n 0 π)(where n 0 is the areal density) and the frequency ω 0 = (2πQ 2 n 0 /ma) 1/2 , to be distinguished from the kdependent 2D analogon of the plasma frequency,In thermodynamic equilibrium, the system is fully characterized by three parameters -the dimensionless inverse screening length κ = a/λ D , the Coulomb coupling parameter Γ = Q 2 /(ak B T ) and the dimensionless magnetic field strength, β = ω c /ω 0 , with the cyclotron frequency ω c = QB/mc. Eq.(1) is solved by a standard microcanonical MD technique, with data acquisition starting after the system has equilibriated to the desired temperature (Γ). The longitudinal and transverse collective excitation spectra, L(k, ω) and T (k, ω), respectively, are computed...

Superdiffusion of two-dimensional Yukawa liquids due to a perpendicular magnetic field

“…For comparison, in Fig. 5(b) we also show the peak frequencies obtained from the frictionless simulation of [46].…”

“…This fit shows how the peak frequency is always greater than the cyclotron frequency. For comparison, we also plot the data from the frictionless simulation of [46] for the peak frequency of the longitudinal waves at the wave number of ka = 5.55.…”

“…There are at least three magnetized dusty plasma devices [41][42][43], which now, or soon will be, producing experimental data. The prospects for these experiments has motivated simulations, including [44][45][46][47], to study waves for 2D Yukawa liquids and solids under a magnetic field. In this literature, the magnetic field strength is quantified by a ratio of the cyclotron and plasma frequencies for dust particles, β = ω c /ω pd .…”

Dynamics of two-dimensional one-component and binary Yukawa systems in a magnetic field

“…Some aspects of the one-component dust particle dynamics in a magnetic field have been considered in previous studies [5,9,11,[14][15][16][17]. In particular, the motion of few-particle clusters in magnetic fields has been studied both by experiments and simulation [10,12].…”

“…Complex plasmas [5][6][7] which contain mesoscopic dust grains are ideal model systems to follow the dynamics on the time and length scale of the individual particles. Typically the dust particles are highly charged such that there are strong repulsive effective interactions between neighbors.…”