Equilibrium crystal shapes in the Potts model

The three-dimensional $q$-state Potts model, forced into coexistence by fixing the density of one state, is studied for $q=2$, 3, 4, and 6. As a function of temperature and number of states, we studied the resulting equilibrium droplet shapes. A theoretical discussion is given of the interface properties at large values of $q$. We found a roughening transition for each of the numbers of states we studied, at temperatures that decrease with increasing $q$, but increase when measured as a fraction of the melting temperature. We also found equilibrium shapes closely approaching a sphere near the melting point, even though the three-dimensional Potts model with three or more states does not have a phase transition with a diverging length scale at the melting point.Comment: 6 pages, 3 figures, submitted to PR

Improvement of reflection electron microscopy : LODREM

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The overheating of lead crystals

Overheating of crystals has scarcely been reported unlike undercooling which is frequently observed. Admittedly the absence of overheating is the consequence of the crystal surface being covered by a liquid film (surface premelting) well under the bulk melting temperature. In the present letter we show that overheating is possible, and is actually observed (ΔT ∼ 3°C), when the crystals are bounded by non wettable facets ({111} facets) separated by relatively small curved regions covered by their melt.Contrairement à la surfusion qui est très fréquemment observée, la surchauffe de cristaux métalliques n'a que rarement été signalée. L'explication généralement avancée est que la surface des cristaux est recouverte d'un film liquide (préfusion de surface) bien avant que la température de fusion volumique ne soit atteinte. Le but de cette courte note est de montrer que la surchauffe est possible et peut effectivement être observée (ΔT ∼ 3°C) lorsque les cristaux sont limités par des faces non mouillées (faces {111}) séparées par des parties courbes de très faible extension recouvertes de leur film liquide