Critical behavior of the thermal conductance of 3He-4He mixture films at the Kosterlitz-Thouless transition

We report measurements of the convective conductance of 3He-4He films near the superfluid transition. This thermal response is tested for the critical behavior observed in pure 4He films. We find that this is preserved for mixtures. The parameters b and D/a2, however, show a strong renormalization, and an unusual 3He dependence. The conductance at fixed T-T/sub c/ decreases upon addition of 3He implying a decrease of the 2D correlation length. We observe a decrease in the maximum value of conductance which we attribute to a residual free-vortex density, even for T