Anisotropy-induced Inhomogeneous Melting in Finite Dust Clusters

Abstract

We present the first experimental evidence of inhomogeneous melting in a finite dusty plasma crystal confined in an anisotropic potential well. By systematically tuning the confinement anisotropy and applying controlled laser heating, distinct melting patterns are observed. Spectral-mode analysis based on Singular Value Decomposition of particle trajectories reveals that increasing laser power redistributes energy into specific collective modes, triggering localized structural destabilization. Molecular Dynamics simulations reproduce the observations and show that confinement-controlled mode coupling with laser heating governs the melting dynamics. These results establish geometric anisotropy as a key control parameter for inhomogeneous melting in finite coupled systems.

Figures (7)

• Figure 1: (a) Schematic illustration of the experimental setup. (b) Top view of the lower electrode showing a central channel of width $d$, within which the particles are confined and externally driven by a collimated green laser beam.
• Figure 2: Experimentally obtained cluster of seven-particles for (a) $\alpha\sim1$, (b) $\alpha = 0.37$, (c) $\alpha = 0.1$ and (d) $\alpha = 0.01$.
• Figure 3: Particle trajectories of a nearly isotropic crystal containing seven particles ($\alpha \sim 1$) under progressively increasing laser power (a–-d); for $\alpha = 0.37$ (e–-h); for $\alpha = 0.1$ (i–-l); and for $\alpha = 0.01$ (m–-p). In each panel, trajectories are recorded over 56 s. The distance between adjacent ticks is 1 mm.
• Figure 4: Variation of the Lindemann's parameter ($\delta$) with laser powers for $\alpha =0.1$. The vertical red dashed line is indicating the transition point at which the crystal undergoes melting.
• Figure 5: Particle trajectories from Langevin Dynamics simulations of a seven-particle anisotropically confined Yukawa system at three values of $\alpha$, corresponding to progressively increasing laser power: (a–d) $\alpha = 1$, (e-h) $\alpha = 0.1$, and (i–l) $\alpha = 0.05$. The trajectories are shown for $\sim$ 56 seconds. The distance between adjacent ticks in the figures is 1 mm.