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λ点

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比热容和不同温度的图

λ点从一般流体氦(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]

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公式表示,其中是对比温度(reduced temperature),是Λ点温度,是常数(在形变点前和形变点后各有一组值),α临界指数[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

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参考资料

  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 [2024-01-22]. doi:10.36471/JCCM_January_2020_02可免费查阅. (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. 

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