⁴He Confined in 0.0483 μm Planar Geometry, Specific Heat and Scaling Near T_λ

We report new specific heat data for ⁴He confined between two silicon wafers at 0.0483 μm separation. This extends our work by a factor of two in the range of confinements studied, and allows us a better check on scaling predictions. The present data have been obtained with a new design for the SiO₂ pattern which is used to achieve the wafer's separation. With this, we have obtained reliable data in the region where the confined helium becomes superfluid. We find that for T>T_λ the new data collapse well onto a universal function. Below T_λ, but above the specific heat maximum, the data also collapse well. Near the maximum, however, there is lack of collapse which persists into the superfluid region. It seems likely that this is connected with the two-dimensional crossover for the geometry of these cells.