We have made heat capacity measurements of superfluid 4He at temperatures very close to the lambda point, Tλ, in a constant heat flux, Q, when the helium sample is heated from above. In this configuration the helium enters a self-organized (SOC) heat transport state at a temperature TSOC(Q), which for Q ≥ 100 n W/cm2 lies below Tλ. At low Q we observe little or no deviation from the Q = 0 heat capacity up to TSOC(Q); beyond this temperature the heat capacity appears to be sharply depressed, deviating dramatically from its bulk behaviour. This marks the formation and propagation of a SOC/superfluid two phase state, which we confirm with a simple model. The excellent agreement between data and model serves as an independent confirmation of the existence of the SOC state. As Q is increased (up to 6 μ W/cm2) we observe a Q dependent depression in the heat capacity that occurs just below TSOC(Q), when the entire sample is still superfluid. This is due to the emergence of a large thermal resistance in the sample, which we have measured and used to model the observed heat capacity depression. Our measurements of the superfluid thermal resistivity are a factor of ten larger than previous measurements by Baddar et al.
|Number of pages||11|
|Journal||Journal of Low Temperature Physics|
|State||Published - Jan 2004|