Thermal Conductivity and Critical Boundary Resistance of Helium Near the Lambda Point

We report measurements of the temperature dependence of the thermal conductivity of helium in the region just above the lambda point and the critical boundary resistance on both sides of the transition. The data were obtained using a cell with a gap that was varied from 0.12 to 0.73 mm. The range of the data was from about 2 mK below to 8 mK above the transition, with a maximum resolution of about 5×10⁻⁹ K, well within the gravity rounded region. We find good agreement with the expected behavior of the thermal conductivity based on the dynamic renormalization group theory. The boundary resistance results above the transition are in fair agreement with the theoretical prediction of Frank and Dohm. Below the transition the wide range results are in approximate agreement with additional predictions and other measurements at higher powers. Closer to the transition on the low temperature side phenomena are observed which appear to be apparatus-dependent.