SUPERFLUID DENSITY FROM HEAT-PULSE PROPAGATION NEAR THE LAMBDA LINE IN HE-4-AEROGEL SYSTEMS

We determined the superfluid density-rho-s from the speed of heat pulses, using a hydrodynamic model that contains coupling between the aerogel and the helium. To investigate the universality of the exponent of rho-s, measurements of rho-s were taken from saturated vapor pressure to 29 bars. Fitting rho-s with a pure power law in reduced temperature leads to a pressure-dependent exponent. Inclusion of a confluent singular term in the fits reveals a pressure-independent exponent-zeta = 0.755 +/- 0.003 which differs from zeta = 0.672 for bulk helium.