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

We consider two-dimensional Yukawa systems in a perpendicular magnetic field. Computer simulations of both one-component and binary systems are used to explore the equilibrium particle dynamics in the fluid state. The mobility is found to scale with the inverse of the magnetic field strength (Bohm diffusion), for strong fields (${\omega }_c/{\omega }_p\gtrsim 1$). For bidisperse mixtures, the magnetic field dependence of the long-time mobility depends on the particle species, providing an external control of their mobility ratio. At large magnetic fields, the highly charged particles are almost immobilized by the magnetic field and form a porous matrix of obstacles for the mobile low-charge particles.

Figure 1

Pair distribution functions and particle trajectories during time ${\omega }_{p}t=30$ at $\Gamma =30$, $\beta =0.5$. Left: One-component system. Right: Binary mixture with $Q_r=4$ and $n_r=1/3$. The highly charged particles are shown in red (gray).

Figure 2

MSD of a one-component system with $\Gamma =100$ at different magnetic field strengths. The straight lines indicate linear and quadratic growth. The order of the curves is the same as in the key.

Figure 3

Top: $D^{*}$ as a function of $\beta$ for values of $\Gamma$ as indicated in the figure. The dotted lines show a decay ${\beta }^{-1}$ as a guide for the eye. Bottom: $D^{*}$ normalized by the field-free value $D_0^{*}=D^{*}\left(0\right)$. The normalized values fall on a universal curve for all values of $\Gamma$.

Figure 4

MSD of a binary system with $n_r=1$, $Q_r=0.5$, and $\Gamma =100$ at different magnetic field strengths. The lower of each pair of curves corresponds to the more highly charged particles. The straight lines indicate linear and quadratic growth. The order of the curves is the same as in the key.

Figure 5

$D^{*}$ as a function of $\beta$ for binary systems with charge ratio $Q_r=0.5$ and $Q_r=0.2$. The lower one of each pair of curves corresponds to the more highly charged species. The dotted lines show a decay ${\beta }^{-1}$ as a guide for the eye.

Figure 6

Ratio $D_2^{*}/D_1^{*}$ for $\Gamma =100,160$ (top) and $\Gamma =30$ (bottom) at different charge ratios $Q_r$ as a function of $\beta$. The right axis in the top graph shows the relative change for $Q_r=0.2,\Gamma =100$, normalized to $\beta =0$.

Figure 7

Ratio $D_2^{*}/D_1^{*}$ as a function of $\Delta =r_{L,2}/\sqrt{n_1}$. Note that small values of $\Delta$ correspond to large magnetic fields, and vice versa.