FREE-ENERGY AND SPECIFIC-HEAT OF CRITICAL FILMS

Based on the field-theoretical renormalization group theory for O(N) symmetric systems in 4 - epsilon dimensions the free energy of critical films confined between two parallel plates at distance L is analyzed. For temperatures above T(c,bulk) the universal scaling functions THETA are presented and discussed. At bulk criticality the scaling functions reduce to the universal Casimir amplitudes. Using these field-theoretical results quantitative predictions on the specific heat of He-4 films and films of He-3 -He-4 mixtures close to the onset of superfluidity are made. Wetting of a substrate by He-4 or He-3 -He-4 mixtures close to the lambda - transition is studied in detail and thus the full scaling function THETA is probed.