COULOMB-SYSTEMS SEEN AS CRITICAL SYSTEMS - FINITE-SIZE EFFECTS IN 2 DIMENSIONS

It is known that the free energy at criticality of a finite two-dimens ional system of characteristic size L has in general a term which beha ves like log L as L --> infinity; the coefficient of this term is univ ersal. There are solvable models of two-dimensional classical Coulomb systems which exhibit the same finite-size correction (except for its sign) although the particle correlations are short-ranged, i.e., non-c ritical. Actually, the electrical potential and electrical field corre lations are critical at all temperatures (as long as the Coulomb syste m is a conductor), as a consequence of the perfect screening property of Coulomb systems. This is why Coulomb systems have to exhibit critic al finite-size effects.