科研之友
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摘要
Below similar to 630 mK, the He-4 atom mass flux F, which passes through a cell filled with solid hcp He-4 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 He-3 concentration, chi = 0.17-220 ppm, to explore the effect of He-3 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. and the T-d (chi) dependence differs somewhat from the predictions for bulk phase separation for T-ps vs chi. We conclude that He-3 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 He-3 concentration or sample history. The universal behavior extrapolates to zero flux in the general vicinity of T-h approximate to 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.
- 出版日期2015-9-14
