Λ点

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比熱容和不同溫度的圖

λ點從一般流體氦(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公式表示,其中是對比溫度(reduced temperature),是Λ点溫度,是常數(在形變點前和形變點後各有一組值),α临界指数[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

相關條目

參考資料

  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. 
  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. 
  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. 
  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. doi:10.36471/JCCM_January_2020_02可免费查阅 (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可免费查阅. 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可免费查阅 (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可免费查阅. 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可免费查阅. 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可免费查阅. doi:10.1007/JHEP06(2020)142. 

外部連結