Superfluid density from heat-pulse propagation near the lambda line in 4He-aerogel systems.

Abstract

We determined the superfluid density ${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$ 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 ${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$, measurements of ${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$ were taken from saturated vapor pressure to 29 bars. Fitting ${\mathrm{\ensuremath{\rho}}}_{\mathit{s}}$ 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 \ensuremath{\zeta}=0.755\ifmmode\pm\else\textpm\fi{}0.003 which differs from \ensuremath{\zeta}=0.672 for bulk helium.