同为氦的同位素,为什么氦-3的超流转变温度比氦-4低了近一千倍?
Both being helium isotopes, why does helium-3 turn superfluid only at temperatures nearly a thousand times lower than helium-4?
差别源于量子统计。⁴He原子是玻色子,可直接向基态凝聚,λ点为2.17 K;³He是费米子,单个原子无从凝聚,必须像超导体中的电子那样先行结成库珀对,液体才能整体进入超流态。其配对依赖微弱的核磁相互作用,形成p波三重态库珀对,耦合很小,BCS机制又使转变温度随耦合强度呈指数下降,结果被压低到毫开量级。这一相变由康奈尔小组在1972年波梅兰丘克压缩冷却的压强曲线突变中发现,随后经核磁共振确证。
The difference lies in quantum statistics. Helium-4 atoms are bosons and condense straight into the ground state, giving a lambda point of 2.17 K, whereas helium-3 atoms are fermions that cannot condense singly; the liquid goes superfluid only after its atoms pair up like electrons in a superconductor. Pairing here rests on feeble nuclear magnetic interactions and takes the form of p-wave triplet Cooper pairs, so the coupling is tiny and BCS physics suppresses the transition temperature exponentially, down to the millikelvin range. Cornell's group discovered this transition in 1972 as abrupt kinks in the pressure record of Pomeranchuk compression cooling, soon confirmed as superfluid by nuclear magnetic resonance.
难度 专业 · 适合 小学高段(9-12)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
D. D. Osheroff、R. C. Richardson 与 D. M. Lee,Physical Review Letters 第28卷885页,1972年
D. D. Osheroff, R. C. Richardson and D. M. Lee, Physical Review Letters 28, 885 (1972)
#超流氦-3 #库珀对 #p波配对
液氦温度降到λ点以下为什么会变成没有黏滞性的超流体?
Why does liquid helium turn into a frictionless superfluid when cooled below the lambda point?
约2.17K以下,⁴He玻色子发生宏观量子凝聚,大量原子占据零动量基态。按朗道两流体模型,液体分为无熵、无黏滞的超流成分与携带熵的正常成分;只要流速低于临界速度,超流无法产生声子或旋子等激发,也就无法耗散能量,于是呈现沿器壁爬行、穿过极细缝隙毫无阻滞等奇异现象。
Below about 2.17 K the bosonic helium-4 atoms undergo macroscopic quantum condensation, with many occupying the zero-momentum ground state. In Landau two-fluid picture the liquid splits into an entropy-free, frictionless superfluid component and a normal component carrying entropy. As long as the flow stays below the critical velocity, the superfluid cannot create phonons, rotons, or other excitations and thus cannot dissipate energy, giving creeping films and unimpeded flow through extremely narrow channels.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-04
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P. 卡皮查,Nature 第141卷74页,1938年;L. D. Landau, J. Phys.(USSR)第5卷71页,1941年
P. Kapitza, Nature 141, 74 (1938); L. D. Landau, J. Phys. USSR 5, 71 (1941)
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1038/141074a0（复合著录按段核验：本标识只担保第一段 P. 卡皮查,
#超流动性 #玻色-爱因斯坦凝聚 #两流体模型
稀释制冷机靠什么实现连续制冷,从而把实验样品长期稳定在毫开尔文温度?
Where does the continuous cooling power of a dilution refrigerator come from, and why can it hold samples steadily at millikelvin temperatures?
冷量来自³He原子溶入超流⁴He时的稀释吸热。约0.87 K以下混合液自发分层:富³He的浓缩相与仍含约6%³He的稀薄相;由于³He在稀薄相中的溶解度即使趋于0 K也不为零,稀薄相就像一台永不干涸的蒸发器。把³He从浓缩相抽运进稀薄相要吸收混合焓,效果等同蒸发热;循环回路再经蒸馏器回收稀薄相中的³He送回混合室,制冷得以持续进行,混合室便稳定在数毫开。
The cooling comes from the heat absorbed when helium-3 atoms dissolve into superfluid helium-4. Below about 0.87 K the mixture separates into a concentrated phase rich in helium-3 and a dilute phase still holding about six percent helium-3; because that solubility stays finite even approaching zero kelvin, the dilute phase behaves as an evaporator that never runs dry. Pumping helium-3 from the concentrated into the dilute phase absorbs the enthalpy of mixing, playing the role of latent heat, while the circulation loop distills helium-3 out of the dilute phase and returns it to the mixing chamber. Cooling therefore runs continuously and the chamber settles at a few millikelvin.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 来源待核验 · Source pending review
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出处备注：此条未指向带版次的可引用著作（通识性内容、机构文件或未展开的英文书名），本库不提供独立书目出处；如需精确引用，需由编辑补全具体篇目与版次。
H. London、G. R. Clarke 与 E. Mendoza,Physical Review 第128卷1992页,1962年
H. London, G. R. Clarke and E. Mendoza, Physical Review 128, 1992 (1962)
#稀释制冷机 #氦-3 #混合焓
无论技术多么先进,为什么物体的温度只能无限逼近绝对零度而永远达不到?
No matter how advanced technology becomes, why can matter only approach absolute zero without ever attaining it?
这正是热力学第三定律的内容:绝对零度只能无限逼近,不可能通过有限次操作到达。制冷的本质是从系统抽走熵,而越接近零开,物质的熵越趋于常数,可抽取的熵越来越少,每一步如绝热去磁所能缩小的温差比例也越来越小,跨越剩余间隔所需的步骤数趋于无穷;再加上低温下难免的热漏与残余气体漏热,样品终会回暖。因此0 K是渐近极限,而不是可达状态。
This is the content of the third law of thermodynamics: absolute zero can be approached arbitrarily closely but never reached in any finite number of operations. Cooling means extracting entropy from a system, yet as zero kelvin nears the entropy of every substance approaches a constant, leaving ever less entropy to remove; each step, such as adiabatic demagnetization, shrinks the remaining gap by a smaller fraction, and the number of steps needed to cross it diverges. Heat leaks and residual-gas conduction, unavoidable at low temperature, keep warming the sample back up. Zero kelvin is thus an asymptotic limit, not an attainable state.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
J. Wilks,The Third Law of Thermodynamics,牛津大学出版社,1961年
J. Wilks, The Third Law of Thermodynamics, Oxford University Press (1961)
独立核验依据 · Independent verification: 核验依据 1 OPENLIBRARY 标识 /works/OL18385987W：The third law of therm
#热力学第三定律 #绝对零度 #绝热去磁
为什么常压下把氦冷却到几乎绝对零度它仍是液体,非要再加大约25个大气压才能变成固体?
Why does helium stay liquid down to nearly absolute zero at ordinary pressure, solidifying only when another twenty-five atmospheres or so are applied?
因为量子零点涨落把原子撑住了。氦的两个电子被闭壳层束缚得极紧,原子最难被极化,原子间范德华引力因此弱于任何其他元素;而原子又非常轻,把它们锁进晶格所需的零点动能超过了这点引力给的收益,晶格无从建立,液体因此无论多冷都保持下来。只有外加约25个大气压压缩原子间距,使排斥与吸引重新平衡,氦才会结晶。
Quantum zero-point motion props the atoms apart. Helium's closed shell binds its two electrons extremely tightly, making the atom the hardest to polarize of any element, so the van der Waals pull between helium atoms is weaker than in any other substance; meanwhile the atoms are so light that pinning one onto a lattice site costs more zero-point kinetic energy than that feeble attraction returns - no crystal can form, whatever the temperature. Only under an extra pressure near twenty-five atmospheres, which squeezes atoms until repulsion and attraction rebalance, does helium freeze.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
J. Wilks 与 D. S. Betts,An Introduction to Liquid Helium,牛津大学出版社,1987年
J. Wilks and D. S. Betts, An Introduction to Liquid Helium, Oxford University Press (1987)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780198514206 (1987)
#零点能 #量子涨落 #氦相图