Solid $$^4$$ 4 He: Progress, Status, and Outlook for Mass Flux Measurements

Abstract

After a brief introduction, what is provided there is brief summary of work with solid 4 He done at the University of Massachusetts Amherst and an outlook for future work. What is presented here is based on a presentation made at the Quantum Gases Fluids and Solids Workshop in Sao Paulo, Brazil in August of 2014. Our work with solid 4 He is aimed at the question: Can a sample cell filled with solid 4 He support a mass flux through the cell? The answer, as will be shown here, is yes. Evidence for this from several types of experiments will be reviewed. There will be an emphasis on more recent work, work that explores how the flux observed depends on temperature and on the 3 He impurity level. The behavior observed suggests that solid 4 He may be an example of a material that demonstrates Bosonic Luttinger liquid behavior. The normalized 4 He flux has a universal temperature dependence. The presence of 3 He at different impurity levels shows that the 3 He blocks the flux at a characteristic temperature. The behavior appears to be consistent with the cores of dislocations as the entity that carries the flux, but it is clear that more work needs to be done to fully understand solid 4 He.

Helium Mass Flow Through a Solid-Superfluid-Solid Junction

“…Neither experiment showed flow at low temperatures. In the second experiment [16], thermally activated vacancy diffusion flow was observed near melting but decreased rapidly with temperature and was undetectable below 500 mK.Recent experiments at the University of Massachusetts (UM) [17,18] have shown unexpected flow at low temperatures and generated considerable interest [19,20]. Chemical potential differences were applied across 4 He crystals, either by transmitting external pressure differences through Vycor "superfluid leads" [17] or by thermally generated fountain pressure gradients along the superfluid leads [18].…”

Dislocation Mobility and Anomalous Shear Modulus Effect in $$^4$$ 4 He Crystals

“…A recent experimental study raised the possibility that dissipative mass flux in solid 4 He could be associated with superfluid cores of edge dislocations [17]. Thus, the question of the presence of superfluid field in solid 4 He has become controversial, as seen on the one hand from the several models mentioned above, that seek to explain the anomalous shear modulus effect without invoking the presence of a superfluid field, and on the other by numerous other studies [14,18,19] which take into account, or discuss the possibility of [20,21,22,23,24] the presence of a superfluid field. Therefore, it seems to us highly pertinent to investigate the effect of an assumed superfluid field on dislocation motion within crystalline 4 He.…”