Mass superflux in solid helium: The role ofHe3impurities

Abstract

Below ∼ 630 mK, the 4 He atom mass flux, F , that passes through a cell filled with solid hcp 4 He in the pressure range 25.6 -26.4 bar, rises with falling temperature and at a temperature T d the flux drops sharply. The flux above T d has characteristics that are consistent with the presence of a bosonic Luttinger liquid. We study F as a function of 3 He concentration, χ = 0.17 − 220 ppm, to explore the effect of 3 He impurities on the mass flux. We find that the strong reduction of the flux is a sharp transition, typically complete within a few mK and a few hundred seconds. Modest concentration-dependent hysteresis is present. We find that T d is an increasing function of χ and the T d (χ) dependence differs somewhat from the predictions for bulk phase separation for Tps vs. χ. We conclude that 3 He plays an important role in the flux extinction. The dependence of F on the solid helium density is also studied. We find that F is sample-dependent, but that the temperature dependence of F above T d is universal; data for all samples scale and collapse to a universal temperature dependence, independent of 3 He concentration or sample history. The universal behavior extrapolates to zero flux in the general vicinity of T h ≈ 630 mK. With increases in temperature, it is possible that a thermally activated process contributes to the degradation of the flux. The possibility of the role of disorder and the resulting phase slips as quantum defects on one-dimensional conducting pathways is discussed.

Mass transport through dislocation network in solid He4

“…Superfluid-like mass flow through 2 cm thick solid 4 He samples sandwiched between superfluid leads was first observed at the University of Massachusetts (UM) [1][2][3][4][5]. This phenomenon was replicated recently at Penn State through solid samples of only 8 µm thick [6].…”

“…One of the most fascinating aspects of this phenomenon is that once the mass flow has been initiated by a pressure difference (∆P ) across the superfluid-solidsuperfluid sandwich by either direct injection of 4 He or by fountain effect, the mass flow rate is not proportional to the diminishing ∆P as in an ordinary fluid; instead, it remains a constant value and ends abruptly when ∆P = 0 [5,6]. This behavior is particularly obvious at low temperatures [6].…”

Saga of Superfluid Solids

“…A different setup was used in the experiments of mass flux measurements [125][126][127][128][129][130][131][132] summarized by Hallock [133]. The idea relies on the fact that superfluid helium in a micro-porous environment at a given temperature freezes at an elevated pressure compared with the freezing pressure for bulk 4 He.…”

“…The earlier assumptions that the flux could be due to liquid channels that can form where crystal boundaries meet a container walls have been ruled out by the present experiments. The superfluid fraction, estimated based on the observed mass flux of the order of a few grams per year [125][126][127][128][129][130][131][132], gives the superfluid fraction at the level of 10 −11 to 10 −10 , under the assumption that the critical velocity is about 10 4 cm/s.…”

“…It is important to emphasize that the superflow through the solid in the flow experiments [125][126][127][128][129][130][131][132][133] has always been observed together with the giant isochoric compressibility regime, or the so-called syringe regime, when atoms of 4 He from liquid are injected into the solid. In flow experiments one looks at the system response when pressure or temperature is changed in one reservoir with liquid Helium by monitoring pressure or temperature in the second reservoir.…”