Superfluidlike mass flow through 2 cm thick solid ${}^4\mathrm{He}$ samples sandwiched between two porous Vycor glass rods filled with superfluid was observed in 2008. The flow commences below 0.6 K, increases in magnitude with decreasing temperature, and shuts off abruptly below a temperature $T_d$ near 0.1 K. $T_d$ is found to increase with ${}^3\mathrm{He}$ impurities at the few parts per million level. The mass flow phenomenon is recently reproduced in $8\mu \mathrm{m}$ thick solid samples; however, the shutoff of mass flow at low temperature is not seen. Here, we report measurements on 2.5 mm thick solid samples. Mass flow rate reduction and extinction near 0.1 K is found only when the concentration of the helium gas, $X_3$, used to prepare the sample exceeds respectively $3.5\times {10}^{-4}$ and $2\times {10}^{-3}$. After the extinction, the mass flow shows a gradual but complete recovery with a characteristic time of many hours. The experimental evidence allows us to formulate a model that explains both the extinction and recovery phenomena. The extinction of the mass flow is due to the trapping of ${}^3\mathrm{He}$ atoms at the nodes or the intersections of the dislocation network which blocks the transport of ${}^4\mathrm{He}$ along the network. The slow recovery in the 2.5 mm samples is due to the migration of the trapped ${}^3\mathrm{He}$ atoms along the dislocation lines and drain into the superfluid inside the porous Vycor glass. Our model also explains naturally the absence of mass flow extinction in the $8\mu \mathrm{m}$ samples and the apparent absence of recovery in the 2 cm samples.

Close

PrevNext

View figure in article

• Diffusion
• Disclinations & dislocations
• Impurities
• Helium-4 superfluids
• Quantum fluids & solids
• Superfluids