Higher harmonics of the magnetoplasmon in strongly coupled Coulomb and Yukawa systems

The generation of higher harmonics of the magnetoplasmon frequency which has recently been reported in strongly coupled two-dimensional Yukawa systems is investigated in detail and, in addition, extended to two-dimensional Coulomb systems. We observe higher harmonics over a much larger frequency range than before and compare the theoretical prediction with the simulations. The influence of the coupling, structure, and thermal energy on the excitation of these modes is examined in detail. We also report on the effect of friction on the mode spectra to make predictions about the experimental observability of this new effect.

Figure 1

$\kappa =2.0$, $\Gamma =200$, $\beta =0.0,0.5,1.0,1.5$ (from top row to bottom row). Left: Collective excitation spectra, $L(k,\omega )+T(k,\omega )$. Right: $L(\omega )$ and $T(\omega )$ at four values of $k$ ($\mathit{ka}=1,2,3,5$, lowest to highest curve).

Figure 2

Combined mode spectrum $L(k,\omega )+T(k,\omega )$ for a) $\kappa =0.0$, $\Gamma =100$ and b) $\kappa =2.0$, $\Gamma =200$, and $\beta =1.0$. Black lines are the theoretical prediction for higher harmonics according to Eq. (13).

Figure 3

$\kappa =2.0,\Gamma =200$, and $\kappa =0.0$, $\Gamma =100$ at $\beta =1.0$, $\mathit{ka}=2.0$. a) The peak position of the $n$th mode. The straight lines are the theoretical predictions (13) with ${\omega }_E/{\omega }_p=0.62$ ($\kappa =0.0$) and ${\omega }_E/{\omega }_p=0.34$ ($\kappa =2.0$). b) The peak intensity normalized to the intensity of the magnetoplasmon ($n=1$). An exponential decay is shown by the straight line.

Figure 4

$\beta =0.7$, $\kappa =2.0$, $\Gamma =10,40,200,1000$ (from top to bottom). Left: Collective excitation spectra, $L(k,\omega )+T(k,\omega )$. Right: $L(k,\omega )+T(k,\omega )$ at two fixed values of $\mathit{ka}=2.0;5.0$ and values of $\Gamma$ as before.

Figure 5

Combined mode spectra at $\mathit{ka}=2.0;5.0$ for identical temperature ($\Gamma =100$) and $\kappa =1.0;2.0;3.0$ (highest to lowest curve), $\beta =1.0$. The curves are shifted vertically for clarity. The inset shows the RPDF $g(r)$.

Figure 6

Combined mode spectra at $\mathit{ka}=2.0;5.0$ for identical structural properties corresponding to ${\Gamma }_{\text{rel}}=0.48$ but different $\kappa =1.0;2.0;3.0$ (highest to lowest curve), $\beta =1.0$. The inset shows the RPDF $g(r)$.

Figure 7

$\Gamma =200$, $\kappa =2.0$, $\beta =0.5$: Combined mode spectra for different values of the friction strength, from $\nu ={10}^{-4}$ (top curve) to $\nu ={10}^{-1}$ (lowest curve).