Oleg Kirichek, Christopher R. Lawson, Christy J. Kinane, Andrew J. Caruana, Sean Langridge, Timothy R. Charlton, Peter V. E. McClintock
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引用次数: 0
摘要
几十年来,超流体氦一直吸引着科学界的兴趣,因为它是一种纯度极高的量子液体,只有在接近绝对零度的温度下才能获得。以前,人们只能用 X 射线直接观测氦薄膜。然而,由于能量沉积水平较高,这种方法仅限于 1 K 以上的温度,而且无法区分氦的同位素。在这里,我们展示了在 170 mK 温度下,相分离混合物薄膜顶部的 3He 层会随着温度的升高逐渐溶解到 4He 中。我们还在 300 mK 附近观察到了薄膜行为的异常现象,并在 1.5 K 时意外地恢复了层状结构,这与 300 mK 附近导致薄膜超流动性被抑制的重入相变是一致的。我们成功地将中子散射应用于研究超低温下的氦薄膜,为未来的研究开辟了新的可能性。超流态是一种表现出无摩擦流动的液体,迄今为止仅限于在低温3He和4He中观察到,其量子态的基本机制非常复杂,而且每种同位素都不相同,因此实验研究超流态现象非常吸引人,但也极具挑战性。作者利用同位素敏感中子反射仪研究了硅表面上的 3He/4He 混合超流氦薄膜,并解析了随着温度变化而出现的结构特征和相变。
Density profile of 3He in a nanoscale 3He-4He superfluid film determined by neutron scattering
For decades, superfluid helium has attracted the interest of the scientific community as an extremely pure realisation of a quantum liquid, only accessible at temperatures close to absolute zero. Previously, helium films have only been observed directly using X-rays. However, this method is limited to temperatures above 1 K due to the high levels of energy deposition, and it also suffers from an inability to distinguish between helium isotopes. Here we show that a 3He layer on top of a phase separated mixture film at 170 mK gradually dissolves into the 4He with increasing temperature. We also observe an anomaly in film behaviour near 300 mK and unexpected restoration of the layered structure at 1.5 K which is consistent with a re-entrant phase transition leading to the suppression of superfluidity in the film near 300 mK. Our successful application of neutron scattering to study helium films at ultra-low temperatures opens up new possibilities for future research. Superfluidity, a liquid exhibiting frictionless flow, is so far limited to observations in low-temperature 3He and 4He, where the underlying mechanisms governing the quantum state are complex and different for each isotope, making for a fascinating but challenging phenomenon to study experimentally. The authors use isotope-sensitive neutron reflectometry to investigate mixed 3He/4He superfluid He films on a Si surface, and resolve the structural features and phase transitions that occur with changing temperature.
期刊介绍:
Communications Physics is an open access journal from Nature Research publishing high-quality research, reviews and commentary in all areas of the physical sciences. Research papers published by the journal represent significant advances bringing new insight to a specialized area of research in physics. We also aim to provide a community forum for issues of importance to all physicists, regardless of sub-discipline.
The scope of the journal covers all areas of experimental, applied, fundamental, and interdisciplinary physical sciences. Primary research published in Communications Physics includes novel experimental results, new techniques or computational methods that may influence the work of others in the sub-discipline. We also consider submissions from adjacent research fields where the central advance of the study is of interest to physicists, for example material sciences, physical chemistry and technologies.