λ点

λ点是氦从一般流体氦(I)相变到超流体氦(II)的温度，在1标准大气压下约为2.17 K。氦（I）和氦（II）可以共存的最低压力是在He气体−He(I)−He(II)的三相点，是在2.1768 K（−270.9732 °C）及5.048 kPa（0.04982 atm），是该温度下的饱和蒸气压（若在气封（英语：Hermetic seal）的容器内，纯氦气会在液体表面形成热平衡）^[1]。氦(I)和氦(II)可以共存的最高压力是立方晶系氦固体−He(I)−He(II)的三相点，位在1.762 K（−271.388 °C）, 29.725 atm（3,011.9 kPa）^[2]。

λ点的名称是因为在上述温度范围内描绘比热容和温度的图时（在上述的压力下，例如一大气压力），会出现希腊文的字母λ。当温度接近λ点时，其比热容会到达其峰值，只有在零重力时才能准确量测到可以说明比热容发散的临界指数（为了要让流体在一体积内的密度是均匀的）。曾在1992年太空船的酬载中量过比λ点低2 nK时的热容^[3]。

未解决的物理问题：说明He-4在超流体形变时热容临界指数

α

理论值和实际值之间的差异原因^[4]

热容的图上有出现峰值，而附近的斜率很大，但在该点的值不会趋近无限大，在形变点前后的值都是有限值^[3]。热容在峰值附近的行为可以用 $C\approx A_{\pm }t^{-\alpha }+B_{\pm }$ 公式表示，其中 $t=|1-T/T_{c}|$ 是对比温度（reduced temperature）， $T_{c}$ 是Λ点温度， $A_{\pm },B_{\pm }$ 是常数（在形变点前和形变点后各有一组值）， $α$ 为临界指数： $\alpha =-0.0127(3)$ ^[3]^[5]。因为在超流体相变时，该指数为负，因此比热仍为有限值

临界指数 $α$ 的实际值和最精准的理论判定技术所得值之间，仍有很大的差异^[6]^[4]，这些技术^[7]^[8]^[9]包括高温膨胀技术、蒙地卡罗方法以及Conformal bootstrapping（英语：Conformal bootstrapping）。

参考资料

^ Donnelly, Russell J.; Barenghi, Carlo F. The Observed Properties of Liquid Helium at the Saturated Vapor Pressure. Journal of Physical and Chemical Reference Data. 1998, 27 (6): 1217–1274. Bibcode:1998JPCRD..27.1217D. doi:10.1063/1.556028.
^ Hoffer, J. K.; Gardner, W. R.; Waterfield, C. G.; Phillips, N. E. Thermodynamic properties of ⁴He. II. The bcc phase and the P-T and VT phase diagrams below 2 K. Journal of Low Temperature Physics. April 1976, 23 (1): 63–102. Bibcode:1976JLTP...23...63H. doi:10.1007/BF00117245.
^ ^3.0 ^3.1 ^3.2 Lipa, J.A.; Swanson, D. R.; Nissen, J. A.; Chui, T. C. P.; Israelsson, U. E. Heat Capacity and Thermal Relaxation of Bulk Helium very near the Lambda Point. Physical Review Letters. 1996, 76 (6): 944–7. Bibcode:1996PhRvL..76..944L. doi:10.1103/PhysRevLett.76.944.
^ ^4.0 ^4.1 Rychkov, Slava. Conformal bootstrap and the λ-point specific heat experimental anomaly. Journal Club for Condensed Matter Physics. 2020-01-31 [2024-01-22]. doi:10.36471/JCCM_January_2020_02 . （原始内容存档于2020-06-09）（英语）.
^ Lipa, J. A.; Nissen, J. A.; Stricker, D. A.; Swanson, D. R.; Chui, T. C. P. Specific heat of liquid helium in zero gravity very near the lambda point. Physical Review B. 2003-11-14, 68 (17): 174518. Bibcode:2003PhRvB..68q4518L. S2CID 55646571. arXiv:cond-mat/0310163 . doi:10.1103/PhysRevB.68.174518.
^ Vicari, Ettore. Critical phenomena and renormalization-group flow of multi-parameter Phi4 theories. Proceedings of the XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007) (Regensburg, Germany: Sissa Medialab). 2008-03-21, 42: 023. doi:10.22323/1.042.0023  （英语）.
^ Campostrini, Massimo; Hasenbusch, Martin; Pelissetto, Andrea; Vicari, Ettore. Theoretical estimates of the critical exponents of the superfluid transition in $^{4}\mathrm{He}$ by lattice methods. Physical Review B. 2006-10-06, 74 (14): 144506. S2CID 118924734. arXiv:cond-mat/0605083 . doi:10.1103/PhysRevB.74.144506.
^ Hasenbusch, Martin. Monte Carlo study of an improved clock model in three dimensions. Physical Review B. 2019-12-26, 100 (22): 224517. Bibcode:2019PhRvB.100v4517H. ISSN 2469-9950. S2CID 204509042. arXiv:1910.05916 . doi:10.1103/PhysRevB.100.224517.
^ Chester, Shai M.; Landry, Walter; Liu, Junyu; Poland, David; Simmons-Duffin, David; Su, Ning; Vichi, Alessandro. Carving out OPE space and precise O(2) model critical exponents. Journal of High Energy Physics. 2020, 2020 (6): 142. Bibcode:2020JHEP...06..142C. S2CID 208910721. arXiv:1912.03324 . doi:10.1007/JHEP06(2020)142.

外部链接

What is superfluidity?

[Donnelly-1] Donnelly, Russell J.; Barenghi, Carlo F. The Observed Properties of Liquid Helium at the Saturated Vapor Pressure. Journal of Physical and Chemical Reference Data. 1998, 27 (6): 1217–1274. Bibcode:1998JPCRD..27.1217D. doi:10.1063/1.556028.

[Hoffer-2] Hoffer, J. K.; Gardner, W. R.; Waterfield, C. G.; Phillips, N. E. Thermodynamic properties of ⁴He. II. The bcc phase and the P-T and VT phase diagrams below 2 K. Journal of Low Temperature Physics. April 1976, 23 (1): 63–102. Bibcode:1976JLTP...23...63H. doi:10.1007/BF00117245.

[JPL-3] 3.0 ^3.1 ^3.2 Lipa, J.A.; Swanson, D. R.; Nissen, J. A.; Chui, T. C. P.; Israelsson, U. E. Heat Capacity and Thermal Relaxation of Bulk Helium very near the Lambda Point. Physical Review Letters. 1996, 76 (6): 944–7. Bibcode:1996PhRvL..76..944L. doi:10.1103/PhysRevLett.76.944.

[Rychkov-4] 4.0 ^4.1 Rychkov, Slava. Conformal bootstrap and the λ-point specific heat experimental anomaly. Journal Club for Condensed Matter Physics. 2020-01-31 [2024-01-22]. doi:10.36471/JCCM_January_2020_02 . （原始内容存档于2020-06-09）（英语）.

[5] Lipa, J. A.; Nissen, J. A.; Stricker, D. A.; Swanson, D. R.; Chui, T. C. P. Specific heat of liquid helium in zero gravity very near the lambda point. Physical Review B. 2003-11-14, 68 (17): 174518. Bibcode:2003PhRvB..68q4518L. S2CID 55646571. arXiv:cond-mat/0310163 . doi:10.1103/PhysRevB.68.174518.

[6] Vicari, Ettore. Critical phenomena and renormalization-group flow of multi-parameter Phi4 theories. Proceedings of the XXV International Symposium on Lattice Field Theory — PoS(LATTICE 2007) (Regensburg, Germany: Sissa Medialab). 2008-03-21, 42: 023. doi:10.22323/1.042.0023  （英语）.

[7] Campostrini, Massimo; Hasenbusch, Martin; Pelissetto, Andrea; Vicari, Ettore. Theoretical estimates of the critical exponents of the superfluid transition in $^{4}\mathrm{He}$ by lattice methods. Physical Review B. 2006-10-06, 74 (14): 144506. S2CID 118924734. arXiv:cond-mat/0605083 . doi:10.1103/PhysRevB.74.144506.

[8] Hasenbusch, Martin. Monte Carlo study of an improved clock model in three dimensions. Physical Review B. 2019-12-26, 100 (22): 224517. Bibcode:2019PhRvB.100v4517H. ISSN 2469-9950. S2CID 204509042. arXiv:1910.05916 . doi:10.1103/PhysRevB.100.224517.

[9] Chester, Shai M.; Landry, Walter; Liu, Junyu; Poland, David; Simmons-Duffin, David; Su, Ning; Vichi, Alessandro. Carving out OPE space and precise O(2) model critical exponents. Journal of High Energy Physics. 2020, 2020 (6): 142. Bibcode:2020JHEP...06..142C. S2CID 208910721. arXiv:1912.03324 . doi:10.1007/JHEP06(2020)142.

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查论编物质状态
状态	固体液体气体 / 蒸气等离子体
低能量	玻色–爱因斯坦凝聚费米凝聚简并态物质量子霍尔效应里德伯物质（英语：Rydberg matter）里德伯极化子（英语：Rydberg polaron）奇异物质超流体超固体光子分子简并态物质超金属
高能量	夸克物质（英语：QCD matter） Lattice夸克（英语：Lattice QCD）夸克-胶子浆奇异物质超临界流体色荷玻璃冷凝物（英语：Color-glass condensate）
其他物态	胶体晶体液晶无定形体玻璃时间晶体准晶体柔粘性结晶（英语：Plastic crystal）磁状态反铁磁性亚铁磁性铁磁性弦状网液态超玻璃暗物质反物质
相变	沸腾沸点临界线（英语：Critical line (thermodynamics)）临界点结晶凝华蒸发闪蒸凝固 λ点熔化熔点复冰现象饱和流体升华过冷三相点清晰点液晶化点二级相变
数量	熔化热升华热汽化热潜热潜内能特鲁顿规则挥发性
概念	双结点（英语：Binodal）压缩流体（英语：Compressed fluid）冷却曲线‎ 状态方程莱顿弗罗斯特现象姆潘巴现象有序与无序（英语：Order and disorder (physics)）调幅分解（英语：Spinodal）超导现象过热蒸汽过热热-电介质效应（英语：Thermo-dielectric effect）
列表	相态列表

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外部链接