Fluidity in Domain Walls in Dilute 3He-4He Films on Graphite: Possible 1D Fermi Fluid and Dirac Fermions in Helium Film
Abstract
The heat capacity of a small amount of 3He atoms dissolved in submonolayer 4He film has been measured. The measured heat capacity is finite and suggests that 3He atoms are mobile at an areal density regime higher than that of the 3×3 phase, where 4He films are believed to be solid. At higher areal densities, the measured heat capacity is proportional to T2 and depends on the amounts of 3He atoms. These behaviors are anomalous to that of a two-dimensional Fermi fluid, and cannot be explained by uniform melting of 4He films. One possible explanation for these anomalous behaviors is that helium atoms exhibit fluidity only inside the domain walls of the adsorption structure, and the dissolved 3He atoms gather into them and behave as a one-dimensional Fermi fluid or as Dirac fermions, depending on the structure of the domain walls. The behaviors of the measured heat capacity strongly suggest this possibility.