Critical behavior of the thermal conductance of He3-He4 mixture films at the kosterlitz-thouless transition

We report measurements of the convective conductance of He3-He4 films near the superfluid transition. This thermal response is tested for the critical behavior observed in pure He4 films. We find that this is preserved for mixtures. The parameters b and Da2, however, show a strong renormalization, and an unusual He3 dependence. The conductance at fixed T-Tc decreases upon addition of He3 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<Tc.