Unexpected observation in measurements of transport coefficients in−43He mixtures nearTλ

Measurements of the shear viscosity η and thermal conductivity κ in four ${}_{}{}^3{}_{}{}^{}\mathrm{-}_{}^4{}_{}{}^{}$He mixtures having ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ concentrations X≤0.09 indicate different λ-transition temperatures for η and κ at the same X. Absent in additional data on pure ${}_{}{}^4{}_{}{}^{}\mathrm{He}$, this difference in transition temperatures increases with ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ concentration. We tentatively attribute the effect to an unexpectedly large enhancement of the ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ concentration near the walls of either the viscometer or the thermal conductivity cell.