Abstract
We use the thermomechanical effect to confirm that a flux of atoms takes place in hcp solid ⁴He below ∼600 mK. We find that the flux falls abruptly in the vicinity of 80 mK and rises with further reduction of temperature. Samples freshly made at 60 mK do not allow mass flux and cannot be grown off the melting curve even when raised in temperature to 200 mK. Solids created above ∼300 mK and cooled to 60 mK can be grown further and demonstrate finite mass flux.