Heat Capacity of Dilute 3He–4He Monolayer Films

The heat capacities of a small amount of 3He dissolved in monolayer 4He films are measured to clarify natures of monolayer 4He films. With increasing areal density, the measured heat capacities gradually increase and subsequently gradually decrease. With further increase in areal density, the measured heat capacity rapidly decreases to zeroover a verynarrowareal density rangenear that of the √ 3×√3phase. These slightly complex areal-density variations and dependence on 3He concentration are discussed from the viewpoint of the known properties of 4He films. The behaviors can be explained. However, the expected two-dimensional gas–liquid or gas–solid coexistence is not observed in this study.