Cooperative Phenomena below Melting of the One-Component Two-Dimensional Plasma

This Letter reports investigations by molecular dynamics of the melting transition of a two-dimensional one-component plasma consisting of 511 particles with logarithmic interactions confined to a disk. Evidence is presented for a weak first-order transition occurring at $T_m=\frac{e^2}{k{\Gamma }_m}$ with ${\Gamma }_m\simeq 142$ and with a melting entropy ≃ 0.17 K. This small entropy is attributed to important premelting phenomena which are cooperative, cyclic permutations of six and more particles as revealed by labeling experiments.