Λ点

λ點是氦從一般流體氦(I)相變到超流體氦(II)的溫度，在1标准大气压下約為2.17 K。氦（I）和氦（II）可以共存的最低壓力是在He氣體−He(I)−He(II)的三相点，是在2.1768 K（−270.9732 °C）及5.048 kPa（0.04982 atm），是該溫度下的飽和蒸氣壓（若在氣封（英语：Hermetic seal）的容器內，純氦氣會在液體表面形成熱平衡）^[1]。氦(I)和氦(II)可以共存的最高壓力是立方晶系氦固體−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點的名稱是因為在上述溫度範圍內描繪比熱容和溫度的圖時（在上述的壓力下，例如一大氣壓力），會出現希腊文的字母λ。當溫度接近λ點時，其比熱容會到達其峰值，只有在零重力時才能準確量測到可以說明比熱容發散的臨界指數（為了要讓流體在一體積內的密度是均勻的）。曾在1992年太空船的酬載中量過比λ點低2 nK時的熱容^[3]。

未解決的物理問題：說明He-4在超流體形變時熱容臨界指數

α

理論值和實際值之間的差異原因^[4]

熱容的圖上有出現峰值，而附近的斜率很大，但在該點的值不會趨近無限大，在形變點前後的值都是有限值^[3]。熱容在峰值附近的行為可以用 $C\approx A_{\pm }t^{-\alpha }+B_{\pm }$ 公式表示，其中 $t=|1-T/T_{c}|$ 是對比溫度（reduced temperature）， $T_{c}$ 是Λ点溫度， $A_{\pm },B_{\pm }$ 是常數（在形變點前和形變點後各有一組值）， $α$ 為临界指数： $\alpha =-0.0127(3)$ ^[3]^[5]。因為在超流體相變時，該指數為負，因此比熱仍為有限值

临界指数 $α$ 的實際值和最精準的理論判定技術所得值之間，仍有很大的差異^[6]^[4]，這些技術^[7]^[8]^[9]包括高溫膨脹技術、蒙地卡羅方法以及Conformal bootstrapping（英语：Conformal bootstrapping）。

參考資料

^ 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.

外部連結

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 / 蒸氣等离子体
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質（英语：Rydberg matter）里德伯極化子（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
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相變	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点熔化熔点復冰現象饱和流体升华过冷三相点清晰點液晶化點二级相变
數量	熔化热升华热汽化热潛熱潜内能特魯頓規則揮發性
概念	双结点（英语：Binodal）压缩流体（英语：Compressed fluid）冷卻曲線‎ 狀態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）
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參考資料

外部連結