Search for Enhancement of the Isobaric Thermal Expansion Coefficient of Superfluid 4He near T λ by a Heat Current

We report an experimental search for the enhancement of the isobaric thermal expansion coefficient (beta (P) ) of superfluid He-4 near the superfluid transition by a heat current (Q). The experiment was carried out using the hot volume technique at constant sample pressure of 1 bar. Liquid helium was contained in a thermal conductivity cell, and a constant heat current, Q=10 or 100 mu W/cm(2), was supplied from below through the sample column. We performed a sample density calculation based on existing helium properties known in the literature and a proposed enhancement Delta beta (P) (Q). Both calculations, with or without the beta (P) enhancement, agree qualitatively with the measurement. The lack of definitive differentiation indicates that the beta (P) enhancement cannot be definitively resolved by our measurement in spite of applications of high-resolution thermometry and pressure regulation.