Safiullin K, Kuzmin V, Stanislavovas A, Alakshin E, Klochkov A, Tagirov M
Institute of Physics, Kazan Federal University, 420008 Kazan, Russia.
Tatarstan Academy of Sciences, 420111 Kazan, Russia.
J Phys Condens Matter. 2020 Feb 10;33(6):065101. doi: 10.1088/1361-648X/abc4f1.
We report on the first observation of He diffusion anisotropy in He-He liquid mixture confined in ordered aerogels at 1.5-4.2 K temperatures. The used aerogels are arrays of long AlO parallel 8 nm strands. The possible origins of diffusion anisotropy are considered and the changes of roton properties introduced by parallel aerogel strands are discussed. Among the responsible mechanisms we account for Knudsen diffusion, potential anisotropy of layer mode excitations or of bulklike excitations, and helium vortices. The observed reduced He diffusion in aerogels is discussed and suggested to appear due to helium excitations at strong confinement conditions. These observations pave the way for future experiments to gain insight into the crossover regime expected at lower temperatures (below 1 K) for which roton density is lower and He collisions with strands play significant role.
我们报道了在1.5 - 4.2 K温度下，限制在有序气凝胶中的氦 - 氦液体混合物中首次观察到的氦扩散各向异性。所使用的气凝胶是由平行排列的8纳米长的AlO链组成的阵列。我们考虑了扩散各向异性的可能起源，并讨论了平行气凝胶链引入的旋子特性变化。在相关机制中，我们考虑了克努森扩散、层模激发或类体激发的势各向异性以及氦涡旋。我们对在气凝胶中观察到的氦扩散降低现象进行了讨论，并认为这是由于在强限制条件下的氦激发所致。这些观察结果为未来的实验铺平了道路，以便深入了解在较低温度（低于1 K）下预期的交叉区域，在该区域旋子密度较低，且氦与链的碰撞起重要作用。
